uals, 


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l°" 

By  WM.  J. 

Surgery  in, 

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nds  of  students.     It  is  issued  in  a  neat  and  attractive  form,  and  at  a  very  reason- 
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No.  3.  MIDWIFERY.  By  ALFRED  LEWIS  GALABIN,  M.A.,  M.D.,  Obstetric 
Physician  to,  and  Lecturer  on  Midwifery  and  the  Diseases  of  Women  at, 
Guy's  Hospital,  London,  etc.  227  fine  Engravings. 

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and  Gynacology,  Trinity  Medical  School,  Toronto. 

No.  4.  PHYSIOLOGY.  Fourth  Edition.  By  GERALD  F.  YEO,  M.D., 
F.R.C.S.,  Professor  of  Physiology  in  King's  College,  London.  Fourth 
American  from  Second  English  Edition.  321  carefully  printed  Illustrations. 

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H.  P.  Bowditch,  Harvard  Medical  School. 

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every  teacher  of  Physiology." — The  Dublin  Journal  of  Medical  Science. 

Jt&-  SEE  NEXT  PAGE.  

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Th 


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No.  5.    ORl 

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THE  LIBRARY 

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'ie  American 

Medical  Assoc, 

PRESENTED  BY 

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on.     With 

an  Index 

PROF.  CHARLES  A.  KOFOID  AND 

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OPINIONS  OF  PROMINENT  MEDICAL  TEACHERS. 

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University,  Cleveland. 

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it  convenient  to  the  study  table  and  handy  fo/  frequent  use.  At  the  same  time  it  is  compre- 
hensive as  to  the  number  of  words,  including  those  of  the  latest  coinage,  and  concise  in  its 
definitions.  The  etymology  and  accentuation  materially  enhance  its  value,  and  help  to  make 
it  worthy  a  place  with  the  classical  books  of  reference  for  medical  students."—./.  W.  Holland, 
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tomical tables  will  be  of  great  use  in  memorizing  the  arteries,  muscles,  etc. 


?  QUIZ-CO M PEN DS.  ?    No.  4. 


COMPEND 


OF 


HUMAN  PHYSIOLOGY 


ESPECIALLY  ADAPTED  FOR  THE  USE  OF 
MEDICAL  STUDENTS. 


BY 


ALBERT  P.  BRUBAKER,  A.M.,  M.  D., 

DEMONSTRATOR   OF     PHYSIOLOGY    IN    THE    JEFFERSON     MEDICAL   COLLEGE;     PROFESSOR 

OF   PHYSIOLOGY,   PENNSYLVANIA   COLLEGE  OF   DENTAL  SURGERY  ;    FELLOW 

OF     THE     COLLEGE     OF     PHYSICIANS     OF     PHILADELPHIA. 


SIXTH    EDITION,    REVISED    AND    IMPROVED. 
WITH  NEW  ILLUSTRATIONS 

AND 

A    TABLE    OF    PHYSIOLOGICAL    CONSTANTS. 

PHILADELPHIA: 

P.    BLAKISTON,    SON    £    CO., 

1012     WALNUT     STREET. 
1891. 


Entered  according  to  Act  of  Congress,  in  the  year  1891,  by 

P.   BLAKISTON,  SON  &  CO., 
In  the  office  of  the  Librarian  of  Congress,  at  Washington,  D.  C. 


PHESS  OF  WM.  F.  FELL  &  Co., 
I22O-24  SANSOM  Sr., 

PHILADELPHIA. 


PREFACE  TO  SIXTH   EDITION. 

It  has  been  deemed  advisable  in  the  preparation  of  a  Sixth  Edition  of 
the  Compend  to  insert  a  number  of  additional  paragraphs  upon  subjects 
which  appeared  to  be  of  interest  and  importance  to  medical  students. 

This  has  accordingly  been  done,  with  the  result  of  increasing  the  size  of 
the  book  some  fifteen  pages.  It  is  hoped  that  the  present  edition  will  even 
more  fully  meet  the  needs  of  the  student. 

ALBERT  P.  BRUBAKER. 


Entered  according  to  Act  of  Congress,  in  the  year  1891,  by 

P.   BLAKISTON,  SON  &  CO., 
In  the  office  of  the  Librarian  of  Congress,  at  Washington,  D.  C. 


PKESS  OF  WM.  F.  FELL  &  Co., 
1220-24  SANSOM  ST., 

PHILADELPHIA. 


PREFACE  TO  SIXTH   EDITION. 

It  has  been  deemed  advisable  in  the  preparation  of  a  Sixth  Edition  of 
the  Compend  to  insert  a  number  of  additional  paragraphs  upon  subjects 
which  appeared  to  be  of  interest  and  importance  to  medical  students. 

This  has  accordingly  been  done,  with  the  result  of  increasing  the  size  of 
the  book  some  fifteen  pages.  It  is  hoped  that  the  present  edition  will  even 
more  fully  meet  the  needs  of  the  student. 

ALBERT  P.  BRUBAKER. 


PREFACE  TO  FIFTH  EDITION. 


In  the  preparation  of  a  Fifth  Edition  of  the  Compend  of  Physiology, 
the  author  has  taken  the  opportunity  to  revise  and  rewrite  a  number  of 
sections,  to  insert  a  few  figures  and  to  add  some  seventeen  pages  of  new 
matter  which,  it  is  hoped,  will  further  increase  its  usefulness  to  the  student. 
While  many  of  the  changes  that  have  been  made  will  be  found  distributed 
throughout  the  body  of  the  work,  the  principal  additions  will  be  found  in 
the  sections  pertaining  to  the  nervous  system. 

Notwithstanding  the  many  additions  which  have  been  made  in  this  and 
previous  editions,  care  has  been  taken  to  keep  the  Compend  what  it  was 
originally  intended  to  be,  viz:  A  compact  and  convenient  arrangement  of 
the  fundamental  facts  of  human  physiology. 

As  most  medical  students  enter  upon  the  study  of  physiology  before  they 
have  acquired  a  thorough  knowledge  of  anatomy,  it  was  thought  desirable 
that  such  anatomical  details  should  also  be  inserted  as  would  be  essential 
to  a  clear  conception  of  the  functions  about  to  be  studied.  It  is  believed 
that  it  will  be  practically  useful  to  students  during  their  attendance  upon 
lectures  and  in  reviewing  the  subject  prior  to  examinations. 

To  those  teachers  of  physiology  who  have  kindly  noticed  and  recom- 
mended the  Compend  to  their  students  I  tender  my  thanks,  and  trust  that 
in  its  improved  condition  it  will  continue  to  merit  their  approval. 

ALBERT  P.  BRUBAKER. 


TABLE  OF  CONTENTS. 


PAGE 

INTRODUCTION, 9 

CHEMICAL  COMPOSITION  OF  THE  BODY, 10 

STRUCTURAL  COMPOSITION  OF  THE  BODY, 17 

FOOD, 19 

DIGESTION, 24 

ABSORPTION, 37 

BLOOD, 45 

CIRCULATION  OF  BLOOD, 51 

RESPIRATION, 59 

ANIMAL  HEAT, 67 

SECRETION, t 69 

Mammary  Glands, 72 

Vascular  or  Ductless  Glands, 74 

EXCRETION, 76 

Kidneys, 76 

Liver,    . 83 

Skin, 88 

NERVOUS  SYSTEM, 92 

Properties  and  Functions  of  Nerves, 95 

Cranial  Nerves, 102 

Spinal  Cord, 116 

Spinal  Nerves, 118 

Medulla  Oblongata, '127 

Pons  Varolii, 131 

Crura  Cerebri, 131 

Corpora  Quadrigemina, 132 

Corpora  Striata  and  Optic  Thalami, 133 

vii 


Vlii  TABLE   OF   CONTENTS. 

PAGE 

Cerebellum, 134 

Cerebrum, 136 

Sympathetic  Nervous  System, 147 

SENSE  OF  TOUCH, 151 

SENSE  OF  TASTE, 152 

SENSE  OF  SMELL, 154 

SENSE  OF  SIGHT, 154 

SENSE  OF  HEARING, 165 

VOICE  AND  SPEECH, 173 

REPRODUCTION, 176 

Generative  Organs  of  the  Female, 176 

Generative  Organs  of  the  Male, 179 

Development  of  Accessory  Structures, 180 

Development  of  the  Embryo, 185 

TABLE  OF  PHYSIOLOGICAL  CONSTANTS, 191 

TABLE  SHOWING  RELATION  OF  WEIGHTS  AND  MEASURES  OF  THE 
METRIC  SYSTEM  TO  APPROXIMATE  WEIGHTS  AND  MEASURES 

OF  THE  U.  S., 194 

INDEX, 195 


COMPEND 

OF 

HUMAN  PHYSIOLOGY. 


Physiology,  from  (pvaig,  nature,  and  Adyof,  a  discourse,  in  its  original 
application  embraced  the  study  of  all  natural  objects,  inorganic  as  well  as 
organic.  In  its  modern  application  physiology  signifies  the  study  of  life  ; 
the  investigation  of  the  vital  phenomena  exhibited  by  all  organic  bodies, 
vegetable  and  animal. 

It  may  be  divided  into — 

1.  Vegetable  physiology ',  which  treats  of  the  phenomena  manifested  by 
the  several  structures  of  which  the  plant  is  composed. 

2.  Animal  Physiology,  which  treats  of  the  phenomena  manifested  by  the 
organs  and  tissues  of  which  the  animal  body  is  composed. 

Human  Physiology  is  the  study  of  the  functions  exhibited  by  the 
human  body  in  a  state  of  health. 

A  function  is  the  action  of  an  organ  or  tissue. 

The  Functions  of  the  Human  Body  may  be  classified  into  three 
groups,  viz. : — 

1.  Nutritive  functions,  which  have  for  their  object  the  preservation  of 
the  individual;  e.  g.,  digestion,  absorption,  circulation  of  the  blood, 
respiration,  assimilation,  animal  heat,  secretion  and  excretion. 

2.  Animal  functions,  which  bring  the  individual  into  conscious  relation- 
ship with  external  nature;  e.g.,  sensation,  motion,  language,  mental 
and  moral  manifestations. 

2.  Reproductive  function,  which  has  for  its  object  the  preservation  of 

the  species. 

The  facts  of  human  physiology  have  been  determined  by  means  of 
anatomy,  chemistry,  pathology,  comparative  anatomy,  vivisection,  the 
application  of  physics,  etc. 

The  body  may  be  studied  from  a  chemical  and  structural  point  of  view. 
B  9 


10  HUMAN   PHYSIOLOGY. 

CHEMICAL  COMPOSITION  OF  THE  HUMAN 
BODY. 

By  chemical  analysis  the  solids  and  fluids  of  the  body  can  be  first 
reduced  to  a  number  of  compound  substances  which  are  termed  proximate 
principles :  these  again  can  be  resolved  by  an  ultimate  analysis  into  fifteen 
chemical  elements.  The  different  chemical  elements  thus  obtained,  and 
the  proportions  in  which  they  exist,  are  shown  in  the  following  table : — 

Oxygen  .    .    .  72.00  "]  O.H.  and  C.  are  found  in  all  the  tissues  and 

Hydrogen  .    .    9.10  !      fluids  of  the  body,  without  exception. 

Nitrogen     .    .    2.50  {  O.  H.  C.  and  N.  found  in  most  of  the  fluids 

Carbon   ...  13-50  j       and  all  tissues  except  fat. 

Sulphur  .  .  .  .147  ...  In  fibrin,  casein,  albumin,  gelatin;  as  potas- 
sium sulpho-cyanide  in  saliva;  as  alkaline 
sulphate  in  urine  and  sweat. 

Phosphorus  .  1.15  ...  In  fibrin  and  albumin;  in  brain;  as  tri-sodium 
phosphate  in  blood  and  saliva,  etc. 

Calcium  .  .  1.30  ...  As  calcium  phosphate  in  lymph,  chyle,  blood, 
saliva,  bones  and  teeth. 

Sodium  ...  .10  ...  As  sodium  chloride  in  all  fluids  and  solids  of 
the  body,  except  enamel ;  as  sodium  sulphate 
and  phosphate  in  blood  and  muscles. 

Potassium  .  .  .026  ...  As  potassium  chloride  in  muscles;  generally 
found  with  sodium  as  sulphates  and  phos- 
phates. 

Magnesium  .  .001  .  .  .  Generally  in  association  with  calcium,  as  phos- 
phate, in  bones. 

Chlorine  .  .  .085  ...  In  combination  with  sodium,  potassium  and 
other  bases,  in  all  the  fluids  and  solids. 

Fluorine     .    .       .08    .    .    .As  calcium  fluoride  in  bones,  teeth  and  urine. 

Iron 01     ...  In  blood  globules ;  as  peroxide  in  muscles. 

Silicon    ...  a  trace  ...  In  blood,  bones  and  hair. 

Manganesium  a  trace  .    .    .  Probably  in  hair,  bones  and  nails. 

Of  the  four  chief  elements  which  together  make  up  gj  per  cent,  of  the 
body,  O.  H.  N.  are  eminently  mobile,  elastic,  and  possess  great  atomic  heat. 
C.  H.  N.  are  distinguised  for  the  narrow  range  and  feebleness  of  their 
affinities  and  chemical  inertia.  C.  has  the  greatest  atomic  cohesion.  O.  is 
noted  for  the  number  and  intensity  of  its  combinations,  and  its  remarkable 
display  of  chemical  activity. 

Chemical  elements,  with  the  exception  of  the  gases,  O.  H.  and  N., 
do  not  exist  alone  in  the  body,  but  are  combined  in  characteristic  propor- 
tions to  form  compounds,  the proxi mate princ {files,  the  ultimate  compounds 
to  which  the  fluids  and  solids  can  be  reduced. 


CHEMICAL  COMPOSITION  OF  THE  HUMAN  BODY.  11 

Proximate  Principles  exist  in  the  body  under  their  own  form,  and  can 
be  extracted  without  losing  their  distinctive  properties. 

There  are  about  one  h-undred  proximate  principles,  which  are  divided 
into  four  classes,  viz  :  inorganic,  organic  non-nitrogenized,  organic  nitro- 
genized,  and  principles  of  waste. 

I.  INORGANIC  PROXIMATE  PRINCIPLES. 

SUBSTANCE.  WHERE   FOUND. 

Oxygen,   .........  Lungs  and  blood. 

Hydrogen,  ........  Stomach  and  intestines. 

Nitrogen,  ......        .    .  Blood  and  intestines. 

Carbonic  anhydride,   ....  Expired  air  of  lungs. 


Water,  ..........  Found  in  all  solids  and  fluids. 

Sodium  chloride,  ......  In  all  fluids  and  solids  except  enamel. 

Potassium  chloride,  .....  In  muscles,  liver,  saliva,  gastric  juice,  etc. 

Ammonium  chloride,  ....  Gastric  juice,  saliva,  tears,  urine. 

Calcium  chloride,   .....  Bones,  teeth,  urine. 

Calcium  carbonate,  .....  Bones,  teeth,  cartilage,  internal  ear,  blood. 

Calcium  phosphate,        "] 

SllhVph^'  [  •    •    I-l,  fluids  and  solids  of  the  body. 

Potassium  phosphate,     J 

Sodium  sulphate,  |  TT  .          ,  M1    ,.,         ,       .... 

Potassium  sulphate,        }  '    '    Umversal  exCePl  milk»  blle  and  SastnC  JU1Ce' 

Sodium  carbonate,         ")  ,  ,      ,   ,        , 

Potassium  carbonate,     }  '    •    Bones,  blood,  lymph,  urine,  etc. 

Magnesium  carbonate,    .    .    .    Blood  and  sebaceous  matter. 

Oxygen  is  one  of  the  constituent  elements  of  all  the  fluids  and  solids  of 
the  body.  It  is  found  in  a  free  state  in  the  respiratory  passages  and  intesti- 
nal tract  ;  it  is  held  in  solution  in  the  lymph  and  plasma  and  forms  a  loose 
combination  with  the  haemoglobin  of  the  blood  corpuscles.  The  function 
of  the  oxygen  in  the  body  appears  to  be  the  oxidation  of  albuminous,  ole- 
aginous and  saccharine  compounds  to  their  ultimate  forms,  urea,  carbonic 
acid,  water,  etc.  As  to  whether  this  is  brought  about  by  direct  oxidation 
or  by  a  fermentative  process  is  yet  unknown.  .As  oxygen  only  enters  into 
combination  under  a  high  temperature,  it  is  assumed  that  it  exists  in  the 
body  under  the  form  of  ozone,  O3,  which  possesses  remarkably  active  oxid- 
izing powers.  The  seat  of  oxidation  is  at  present  located  in  the  tissues,  as 
the  presence  of  ozone  in  the  blood  has  not  been  positively  demonstrated. 

Hydrogen  is  also  a  constituent  element  of  almost  all  the  compounds  of 
the  body;  it  exists  in  a  free  state  in  the  intestinal  tract,  where  it  is  produced 


12  HUMAN   PHYSIOLOGY. 

by  a  decomposition  of  organic  substances ;  it  is  also  produced  within  the  tis- 
sues as  a  result  of  chemical  changes.  Its  function  is  unknown,  though  it  is 
asserted  by  Hoppe-Seyler  that  hydrogen  unites  with  neutral  oxygen,  O2,  in 
the  tissues,  forming  water  and  liberating  oxygen  in  the  nascent  state,  which 
becomes  the  oxidizing  agent.  The  process  is  represented  in  the  following 
equation : — 

HH  -f-  O2  -f  n  =  H2O  +  On, 

in  which  n  represents  the  oxidizable  substance. 

Water  is  an  essential  constituent  of  all  the  tissues  of  the  body,  consti- 
tuting about  70  per  cent,  of  the  entire  body  weight.  It  is  introduced  into 
the  body  in  the  form  of  drink  and  as  a  constituent  of  all  kinds  of  food. 
The  average  quantity  consumed  daily  is  about  four  pints.  While  in  the 
body,  water  acts  as  a  general  solvent,  gives  pliability  to  various  tissues,  and 
promotes  the  passage  of  inorganic  and  organic  matters  through  animal 
membranes.  It  also  promotes  chemical  changes  which  are  essential  to 
absorption  and  assimilation  of  food  and  the  elimination  of  products  of 
waste.  It  is  probable  that  water  is  also  formed  within  the  body  by  the 
union  of  oxygen  with  the  surplus  hydrogen  of  the  food.  It  is  eliminated 
by  the  skin,  lungs  and  kidneys. 

Sodium  Monde  is  present  in  all  the  solids  and  fluids  of  the  body,  with 
the  exception  of  enamel.  It  regulates  osmotic  action,  holds  the  albuminous 
principles  of  the  blood  in  solution,  and  preserves  the  form  and  consistence 
of  blood  corpuscles  and  the  cellular  elements  of  the  tissues,  by  regulating 
the  amount  of  water  entering  into  their  composition. 

Calcium  phosphate  is  the  most  abundant  of  all  the  inorganic  principles 
with  the  exception  of  water,  and  is  present  to  a  great  extent  in  bone,  teeth, 
muscles  and  milk.  It  gives  the  requisite  consistency  and  solidity  to  the 
different  tissues  and  organs.  In  the  blood,  it  is  held  in  solution  by  the 
albuminous  constituents. 

The  Sodium  and  Potassium  phosphates  are  present  in  most  of  the  solids 
and  fluids,  and  give  to  them  their  alkaline  reaction.  They  are  chiefly 
derived  from  the  food. 


II.  ORGANIC  NON-NITROGENIZED  PRINCIPLES. 
The  organic  non-nitrogenized  principles  are  derived  mainly  from  the 
vegetable  world,  but  are  also  produced  within  the  animal  body.  They  are 
divided  into  :  1st,  the  carbo-hydrates,  comprising  starch  and  sugar,  bodies 
in  which  the  oxygen  and  hydrogen  exfst  in  the  proportion  to  form  water, 
the  amount  of  carbon  being  variable;  2d,  the  fats,  bodies  having  the  same 


CHEMICAL   COMPOSITION    OF   THE   HUMAN   BODY.  13 

elements  entering  into  their  composition,  but  with  the  carbon  and  hydrogen 
increased  and  the  oxygen  diminished  in  amount;  3d,  fatty  acids;  4th,  alco-- 
hols. 

SUGARS.  C.  O.  H. 

Glycogen,  or  Liver  sugar. 
Lactose,      or  Milk  sugar. 
Glucose,     or  Grape  sugar. 
Inosite,       or  Muscle  sugar. 

Sugar  is  found  in  many  of  the  tissues  and  fluids  of  the  body ;  e.g.,  liver, 
milk,  placenta,  blood,  muscles,  etc.  The  varieties  of  sugar  are  soluble  in 
water,  assume  the  crystalline  form  upon  evaporation,  and  are  converted 
into  alcohol  and  carbonic  acid  by  fermentation.  Sugar  is  derived  from  the 
food,  converted,  in  the  alimentary  canal,  into  glucose,  absorbed  by  the  veins 
of  the  portal  system,  and  then  stored  up  in  the  liver,  under  the  form  of 
glycogen.  When  the  system  requires  sugar,  it  is  again  returned  to  the  cir- 
culation, and  plays  its  part  in  the  nutritive  processes  of  the  body.  It  is 
finally  oxidized,  and  thus  contributes  to  the  formation  of  heat.  It  is  finally 
eliminated  under  the  form  of  carbonic  acid  and  water.  There  is  no  experi- 
mental proof  that  sugar  contributes  directly  to  the  formation  of  fat  in  the 
animal  body. 

NEUTRAL  FATS.      C.  O.  H. 

Palmitin. 

Stearin. 

Olein. 

The  Neutral  fats,  when  combined  in  proper  proportions,  constitute  a 
large  part  of  the  fatty  tissue  of  the  body;  they  are  soluble  in  ether,  chloro- 
form and  hot  alcohol;  insoluble  in  cold  alcohol  and  water,  and  liquefy  at 
a  high  temperature;  when  a  neutral  fat  is  subjected  to  a  high  temperature 
in  the  presence  of  water  and  an  alkali,  it  is  decomposed,  with  the  assimi- 
lation of  the  elements  of  water,  into  a  fatty  acid  and  glycerine.  The  fatty 
acid  combines  with  the  alkali  and  forms  an  oleate,  palmitate  or  stearate, 
according  to  the  fat  used.  A  similar  decomposition  of  the  neutral  fats  is 
said  to  take  place  in  the  small  intestine  during  digestion.  When  thoroughly 
mixed  with  pancreatic  juice,  the  fats  are  reduced  to  a  condition  of  emulsion, 
a  state  in  which  the  fat  is  minutely  subdivided  and  the  small  globules  held 
in  suspension. 

FATTY   ACIDS.      C.  O.  H. 

Palmitic  acid.  Propionic  acid. 

Stearic  acid.  Butyric  acid. 

Oleic  acid.      .  Caproic  acid. 


14  HUMAN   PHYSIOLOGY. 

The  Fatty  acids  combined  with  sodium,  potassium  and  calcium,  are 
•found  as  salts  in  various  fluids  of  the  body,  such  as  blood,  chyle,  faeces, 
etc.  Phosphorized  fats  in  nervous  tissue,  butyric  acid  in  milk,  propionic 
acid  in  sweat,  are  also  constituents  of  the  body. 

The  Fats  are  derived  from  the  food,  both  animal  and  vegetable.  They 
are  deposited  in  the  form  of  small  globules  in  the  cells  of  the  different 
tissues,  are  suspended  in  various  fluids,  are  deposited  in  masses  in  and 
around  various  anatomical  structures  and  beneath  the  skin.  Independent 
of  the  fat  consumed  as  food,  there  is  good  experimental  evidence  that  fat 
is  also  produced  within  the  animal  body  from  a  partial  decomposition  of 
the  albuminous  compounds.  Fat  serves  as  a  non-conductor  of  heat,  gives 
roundness  and  form  to  the  body,  and  protects  various  structures  from 
injury.  The  fats  are  ultimately  oxidized,  thus  giving  rise  to  heat  and 
force,  and  are  finally  eliminated  as  carbonic  acid  and  water. 

ALCOHOLS. 

Glycerine.  Cholesterine.  Alcohol. 

Glycerine  is  chemically  a  triatomic  alcohol  in  combination  with  the  neu- 
tral fats  of  the  body.  During  pancreatic  digestion  it  is  set  free.  It  is 
supposed  by  many  physiologists  to  be  directly  concerned  in  the  production 
of  glycogen.  Cholesterine  is  a  crystallizable  substance  largely  present  in 
the  bile,  though  it  is  found  in  other  fluids  and  solids.  It  is  supposed  to  be 
a  waste  product  of  nervous  matter.  Alcohol  has  been  found  in  the  urine. 
It  is  supposed  to  be  the  result  of  an  alcoholic  fermentation  in  the  intestine. 

III.  ORGANIC  NITROGENIZED   PRINCIPLES. 

The  nitrogenized  or proteid  compounds  are  organic  in  their  origin,  being 
derived  from  the  animal  and  vegetable  world ;  they  are  taken  into  the  body 
as  food,  appropriated  by  the  tissues,  and  constitute  their  organic  basis;  they 
differ  from  the  non-nitrogenized  substances  in  not  being  crystalline,  but 
amorphous,  in  having  a  more  complex  but  just  as  definite  composition,  and 
containing  in  addition  to  C.  O.  H.,  nitrogen,  with,  at  times,  sulphur  and 
phosphorus.  The  proteids  possess  characteristics  which  distinguish  them 
from  all  other  substances :  viz.,  a  molecular  mobility,  which  permits  isomeric 
modifications  to  take  place  with  great  facility;  a  catalytic  influence,  in 
virtue  of  which  they  promote,  under  favorable  conditions,  chemical  changes 
in  other  substances:  e.g.,  during  digestion,  salivin  and  pepsin  cause  starch 
and  albumin  to  be  transformed  into  sugar  and  albuminose  respectively. 
Different  proteids  possess  varying  proportions  of  water,  which  they  lose 


CHEMICAL  COMPOSITION   OF  THE   HUMAN  BODY.  15 

when  subjected  to  desiccation,  becoming  solid;  but  upon  exposure  to 
moisture  they  again  absorb  water,  regaining  their  original  condition — they 
are  hygroscopic.  Another  property  is  that  of  coagulation,  which  takes 
place  under  certain  conditions :  e.g.,  the  presence  of  mineral  acids,  heat, 
alcohol,  etc. 

After  death  the  nitrogenized  compounds  undergo  putrefactive  changes, 
give  rise  to  carburetted  and  sulphuretted  hydrogen  and  other  gases.  In 
order  that  these  changes  may  take  place  it  is  essential  that  certain  condi- 
tions be  present:  viz.,  atmospheric  air  or  some  fluid  containing  oxygen, 
moisture,  and  a  temperature  varying  between  60°  and  90°  F.  The  cause 
of  the  putrefactive  change  is  the  presence  of  a  minute  unicellular  organ- 
ism, the  bacterium  termo. 

The  nitrogenized  bodies  found  in  the  organism  are  quite  numerous,  and 
although  they  resemble  each  other  in  many  particulars,  there  are  yet 
important  differences,  and  can  be  arranged  into  the  following  groups  : — 

1.  NATIVE  ALBUMINS. — Proteid  bodies  soluble  in  water,  many  acids,  and 
usually  in  alkalies;  coagulable  at  a  temperature  of  from  140°  to  163°  F. 

a.  Serum  Albumin,  the  principal  form  of  albumin  found  in  the  animal 
fluids  and  solids. 

b.  Egg  albumin,  not  found  in  ordinary  tissues,  but  present  in  white 
of  egg. 

2.  GLOBULINS. — Proteid  bodies  insoluble  in  water,  but  soluble  in  solutions 
of  sodium  chloride. 

a.  Globulin,  found  in  many  tissues,  but  largely  present  in  crystalline 
lens. 

b.  Myosin,  found  in  the  muscles  in   life  in  a  fluid  condition;    after 
death  it  undergoes  coagulation,  giving  rise  to  the  rigidity  of  the 
muscles. 

c.  Paraglobulin,  present  in  blood  and  obtained  from  it  by  passing  a 
stream  of  carbon   dioxide   through  it;    it  is  also   precipitated   by 
adding  sodium  chloride. 

d.  Fibrinogen,  present  in  serous  fluid  and  blood,  and  can  be  precipi- 
tated by  the  prolonged  use  of  carbon  dioxide ;  it  is  also  precipitated 
by  the  addition  of  12  to  1 6  per  cent,  of  sodium  chloride. 

3.  DERIVED  ALBUMINS. — Proteid  bodies  which  are  not  coagulable  by  heat; 
insoluble  in  pure  water  and  in  salt  solutions ;  soluble  in  both  acid  and 
alkaline  solutions. 

a.  Acid  Albumin,  found  principally  in  the  stomach  during  first  stage 
of  digestion,  the  result  of  the  action  of  the  hydrochloric  acid  upon 
the  albumin  of  the  food. 


16  HUMAN   PHYSIOLOGY. 

b.  Alkali  Albumin,  found  in  the  intestine  during  pancreatic  digestion, 
the  result  of  the  action,  of  alkalies  upon  the  albumin  of  the  food. 

c.  Casein,  the  chief  proteid  of  milk ;  it  is  precipitated  by  acetic  acid 
and  rennet. 

4.  PEPTONES. — These  bodies  are   formed  in  the  stomach  and  intestinal 
tract  by  the  action  of  the  gastric  and  pancreatic  juices  upon  the  albumins 
of  the  food.     They  are  very  soluble  in  water,  alkaline  and  acid  solutions ; 
non-coagulable  by  heat;  very  diffusible.     They  are  precipitated  by  tannic 
acid  and  alcohol. 

5.  ALBUMINOIDS. — The  albuminoids  are  the  results  of  various  modifica- 
tions of  albumins  occurring  during  the  nutritive  process,  as  well  as  by 
the  action  of  various  external  influences. 

a.  Mucin,  the   characteristic    ingredient   of  mucus   secreted   by    the 
mucous  membranes,  giving  to  it  its  viscidity. 

b.  Chondrin,  found  in  cartilage. 

c.  Gelatin,  found  in  connective  tissue,  tendons,  ligaments,  bones,  etc. 

d.  Elastin,  found  in  elastic  tissue. 

e.  Keratin,  found  in  skin  and  epidermic  appendages,  nails,  hair,  horn,  etc. 

6.  FIBRIN. — A  filamentous  albumin  obtained  by  washing  blood  clots.     It 
is  insoluble  in  water  and  mineral  acids. 

As  the  properties  of  the  compounds  formed  by  the  union  of  elements  are 
the  resultants  of  the  properties  of  the  elements  themselves,  it  follows  that 
the  ternary  substances,  sugars,  starches  and  fats,  possess  a  great  inertia  and 
a  notable  instability ;  while  in  the  more  complex  albuminous  compounds, 
in  which  sulphur  and  phosphorus  are  united  to  the  four  chief  elements, 
molecular  mobility,  resulting  in  isomerism,  exists  in  a  high  degree.  As 
these  compounds  are  unstable,  of  a  greater  molecular  mobility,  they  are  well 
fitted  to  take  part  in  the  composition  of  organic  bodies,  in  which  there  is 
a  continual  movement  of  composition  and  decomposition. 

IV.  PRINCIPLES  OF  WASTE. 

Urea.  Xanthin,  Sodium,  "1 

Creatin,  Tyrosin,  Potassium,  I    Urates 

Creatinin,  Hippuric  Acid,  Ammonium, 

Cholesterin,  Calcium  Oxalate,  Calcium, 

These  principles  which  represent  waste  are  of  organic  origin,  arising 
within  the  body  as  products  of  disassimilation  or  retrograde  metamorphosis 
of  the  tissues;  they  are  absorbed  by  the  blood,  carried  to  the  various 
excretory  organs,  and  by  them  eliminated  from  the  body. 

The  excrementitious  substances  will  be  fully  considered  under  excretion. 


STRUCTURAL   COMPOSITION   OF  THE   BODY.  17 

Proximate  Quantity  of  the   Chemical   Elements   and   Proximate 
Principles  of   the  Body,  Weighing  154  Ibs. 

Ibs.      07..  Ibs.      oz. 

Oxygen,       in  .  .     Water, in 

Hydrogen, 14  .  .     Albuminoids, 23      7 

Nitrogen, 3  8     Fats, 12 

Carbon,        21  .  .  Calcium  phosphate,  ...       5     13 

Calcium, 2  .  .  Calcium  carbonate,   ...       I 

Phosphorus, I  12     Calcium  fluoride, 3 

Sodium,  etc., 12  Sodium  sulphate,  etc., '.    ...       9 


154     -  .  154 


STRUCTURAL  COMPOSITION  of  THE  BODY. 

The  Study  of  the  Structure  of  the  body  reveals  that  it  is  composed 
of  dissimilar  parts,  e.g.,  bones,  muscles,  nerves,  lungs,  etc.;  while  these, 
again,  by  closer  examination,  can  be  resolved  into  elementary  structures, 
the  tissues,  e.g.,  connective  tissue,  muscular,  nervous,  epithelial  tissue,  etc. 

Microscopical  examination  of  the  tissues  shows  that  they  are  com- 
posed of  fundamental  structural  elements,  termed  cells. 

Cells  are  living  physiological  units  ;  the  simplest  structural  forms  capable 
of  manifesting  the  phenomena  of  life. 

Cells  vary  in  their  anatomical  constitution  in  the  different  structures  of 
the  bocly,  and  may  be  classed  in  three  groups,  viz  :  i.  Cells  possessing  a 
distinct  cell  wall,  cell  stibstance  and  a  nucleus.  2.  Cells  possessing  a  cell 
substance  and  a  nucleus.  3.  Cells  possessing  the  cell  substance  only. 
They  vary  in  size,  from  the  g^Vtf  to  the  ^00  of  an  inch  in  diameter;  when 
young  and  free  to  move  in  a  fluid  medium  they  assume  the  spherical  form; 
but  when  subjected  to  pressure,  may  become  flattened,  cylindrical,  fusiform 
or  stellate. 

Structure  of  Cells.  The  cell  wall  is  not  an  essential  structure,  as 
many  cells  are  entirely  devoid  of  it.  It  is  a  thin,  structureless,  transparent 
membrane,  permeable  to  fluids. 

The  Cell  Substance  in  young  cells  is  a  soft,  viscid,  albuminous  matter, 
unstable,  insoluble  in  water,  and  known  as  protoplasm,  bioplasm,  sarcode, 
etc. ;  in  older  cells  the  original  cell  substance  undergoes  various  transform- 
ations, and  is  partly  replaced  by  fat  globules,  pigment  and  crystals. 

The  Nucleus  is  a  small  vesicular  body  in  the  interior  of  the  cell  sub- 
stance, and  frequently  contains  smaller  bodies,  the  nucleoli. 


18  HUMAN   PHYSIOLOGY. 

MANIFESTATIONS  OF  CELL  LIFE. 

Growth.  Cells  when  newly  formed  are  exceedingly  small,  but  as  they 
approach  maturity  they  increase  in  size,  by  the  capability  which  the  cells 
possess  of  selecting  and  appropriating  new  material  as  food,  vitalizing  and 
organizing  it.  The  extent  of  cell  growth  varies  in  different  tissues;  in 
some  the  cells  remain  exceedingly  small,  in  others  they  attain  considerable 
size.  In  many  instances  the  cell  substance  undergoes  transformation  into 
new  compounds  destined  for  some  ulterior  purpose. 

Reproduction.  Like  all  organic  structures  cells  have  a  limited  period 
of  life ;  their  continual  decay  and  death  necessitates  a  capability  of  repro- 
duction. Cells  reproduce  themselves  in  the  higher  animals  mainly  by 
fission.  This  is  seen  in  the  white  blood  corpuscles  of  the  young  embryos 
of  animals;  the  corpuscle  here  consists  of  a  cell  substance  and  nucleus. 
When  division  of  the  cell  is  about  to  take  place,  the  nucleus  elongates,  the 
cell  substance  assumes  the  oval  form,  a  constriction  occurs,  which  gradually 
deepens,  until  the  original  cell  is  completely  divided  and  two  new  cells  are 
formed,  each  of  which  soon  grows  to  the  size  of  the  parent  cell. 

In  cells  provided  with  a  cell  membrane  the  process  is  somewhat  different. 
In  the  ova  of  the  inferior  animals,  after  fertilization  has  taken  place,  a 
furrow  appears  on  the  opposite  sides  of  the  cell  substance,  which  deepens 
until  the  cell  is  divided  into  two  equal  halves,  each  containing  a  nucleus; 
this  process  is  again  repeated  until  there  are  four  cells,  then  eight,  and  so 
on  until  the  entire  cell  substance  is  divided  into  a  mulberry  mass  of  cells, 
completely  occupying  the  interior  of  the  cell  membrane.  The  whole  pro- 
cess of  segmentation  takes  place  with  great  rapidity,  occupying  not  more 
than  a  few  minutes,  in  all  probability. 

Motion.  Spontaneous  movement  has  been  observed  in  many  of  the 
cells  of  the  body.  It  may  be  studied,  for  example,  in  the  movements  of 
the  spermatozoids,  the  waving  of  the  cilia  covering  the  cells  of  the  bronchial 
mucous  membrane,  the  white  corpuscles  of  the  blood,  etc. 

By  a  combination  and  transformation  of  these  original  structural  elements, 
and  material  derived  from  them,  all  the  tissues  are  formed  which  enter  into 
the  structure  of  the  human  body. 

CLASSIFICATION  OF  TISSUES. 

I.  Homogeneous  Substance,  a  more  or  less  solid,  albuminous  struc- 
ture, filling  the  spaces  between  the  cells  and  fibres  of  various  tissues,  e.g., 
cartilage,  bone,  dentine,  etc. 

II.  Limiting  Membrane,  a  thin  homogeneous  membrane,  structureless, 


FOOD.         '  19 

composed  of  coagulated  albumin,  and  often  not  more  than  the  ^T5tf  °f  an 
inch  in  thickness,  found  lining  the  blood  vessels  and  lymphatics,  forming 
the  basement  membrane  of  the  skin  and  mucous  membranes,  the  posterior 
layer  of  the  cornea,  the  capsule  of  the  crystalline  lens,  etc. 

III.  Simple  fibrous  or  filamentous  tissue — the  elements  of  which 
are  real  or  apparent  filaments. 

(a)  Connective  or  areolar ;   white  fibrous  tissue ;    constituting  tendons, 
ligaments,   aponeuroses,    periosteum,   dura    mater,    synovial    membranes, 
vascular  tunics,  etc. 

(b)  Yellow  elastic  tissue ;  found  in  the  middle  coats  of  arteries,  veins, 
lymphatics,  ligamentum  nuchoe,  vocal  cords,  ligamenta  subflava,  etc. 

IV.  Compound    membranes    (membrano- cellular    or    fibro-cellular 
tissues),  cells  aggregated  into  laminse. 

(a)  Epidermic  tissue ;  (b)  epithelial  tissue ;  (c)  glandular  tissue;  (d) 
cornea. 

V.  Cells  containing  coloring  matter,  or  pigment  cells,  e.  g.,  skin, 
choroid  membrane,  etc. 

VI.  Cells  coalesced  or  consolidated  by  internal  deposits,  e.  g., 
hair,  nails,  bone,  teeth,  etc. 

VII.  Cells  imbedded  in  an  intercellular  substance,  e.  g.,  cartilage, 
crystalline  lens,  etc. 

VIII.  Cells  aggregated  in  clusters,  forming  tissues  more  or  less  solid, 
e.  g.,  adipose  tissue,  lymphatic  glands. 

IX.  Cells  imbedded  in  a  matrix  of  capillaries,  e.  g.,  gray  or  vesicular 
nervous  matter. 

X.  Cells  whose  coalesced  cavities    form   tubes   containing   liquids   or 
secondary  solid  deposits,  e.  g.,  vascular  tissue,  dentine. 

XI.  Cells  free,  isolated,  or  floating— fluid  tissue — e.  g.,  red  and  white 
blood  corpuscles,  lymph  and  chyle  corpuscles. 


FOOD. 

A  Food  may  be  defined  to  be  any  substance  capable  of  playing  a  part 
in  the  nutrition  of  the  body. 

Food  is  required  for  the  repair  of  the  waste  of  the  tissues  consequent  on 
their  functional  activity,  for  the  generation  of  heat  and  the  evolution  of  force. 

Hunger  and  Thirst   are  sensations  which  indicate  the  necessity  for 


20  HUMAN    PHYSIOLOGY. 

taking  food;  they  arise  in  the  tissues  at  large,  and  are  referred  to  the 
stomach  and  fauces,  respectively,  through  the  sympathetic  nervous  system. 

Inanition  or  Starvation  results  from  an  insufficiency  or  absence  of 
food,  the  physiological  effects  of  which  are  hunger,  intense  thirst,  intestinal 
uneasiness,  weakness  and  emaciation;  the  quantity  of  carbonic  acid  ex- 
haled diminishes  and  the  urine  is  lessened  in  amount;  the  volume  of  the 
blood  diminishes;  a  fetid  odor  is  exhaled  from  the  body;  vertigo,  stupor 
followed  by  delirium,  and  at  times  convulsions,  result  from  a  disturbance 
of  the  nerve  centres;  a  marked  fall  of  the  bodily  temperature  occurs,  from 
a  diminished  activity  of  the  nutritive  process.  Death  usually  takes  place, 
from  exhaustion. 

During  starvation  the  loss  of  different  tissues,  before  death  occurs,  aver- 
ages T4^,  or  40  per  cent,  of  their  weight. 

Those  tissues  which  lose  more  than  40  per  cent,  are  fat,  93.3 ;  blood,  75; 
spleen,  71.4;  pancreas,  64.1;  liver,  52;  heart,  44.8;  intestines,  42.4; 
muscles,  42.3.  Those  which  lose  less  than  40  per  cent,  are  the  muscular 
coat  of  the  stomach,  39.7;  pharynx  and  oesophagus  34.2;  skin,  33.3; 
kidneys,  31.9;  respiratory  apparatus,  22.2;  bones,  16.7;  eyes,  10;  nervous 
system,  1.9. 

The  'Fat  entirely  disappears,  with  the  exception  of  a  small  quantity 
which  remains  in  the  posterior  portion  of  the  orbits  and  around  the  kid- 
neys. The  Blood  diminishes  in  volume  and  loses  its  nutritive  properties. 
The  Mtiscles  undergo  a  marked  diminution  in  volume  and  become  soft  and 
flabby.  The  Nervous  system  is  last  to  suffer,  not  more  than  two  per  cent, 
disappearing  before  death  occurs. 

The  appearances  presented  by  the  body  after  death  from  starvation  are 
those  of  anoemia  and  great  emaciation;  almost  total  absence  of  fat;  blood- 
lessness;  a  diminution  in  the  volume  of  the  organs;  an  empty  condition 
of  the  stomach  and  bowels,  the  coats  of  which  are  thin  and  transparent. 
There  is  a  marked  disposition  of  the  body  to  undergo  decomposition, 
giving  rise  to  a  very  fetid  odor. 

The  duration  of  life  after  a  complete  deprivation  of  food  varies  from 
eight  to  thirteen  days,  though  life  can  be  maintained  much  longer  if  a 
quantity  of  water  be  obtained.  The  water  is  more  essential  under  these 
circumstances  than  the  solid  matters,  which  can  be  supplied  by  the  organism 
itself. 

The  food  consumed  daily  is  a  heterogeneous  compound  consisting  of 
both  nutritious  and  innutritious  portions.  The  nutritious  portions  are 
known  as  the  alimentary  principles,  while  the  food,  as  a  whole,  is  known 
as  aliment. 


FOOD.  21 

The  different  alimentary  principles  which  are  appropriated  by  the  system 
are  combined  in  different  proportions  in  the  various  articles  of  food,  and 
are  separated  from  the  innutritious  substances  during  the  process  of  diges- 
tion. They  belong  to  the  organic  and  inorganic  worlds,  and  may  be 
classified,  according  to  their  chemical  composition,  as  follows : — 

CLASSIFICATION  OF  ALIMENTARY  PRINCIPLES. 

1.  Albuminous  group — nitrogenized,  C.  O.  H.  N.  S.  P. 

PRINCIPLE.  WHERE   FOUND. 

Afyosin,  syntonin, Flesh  of  animals. 

Vitellin,  albumin, Yolk  of  egg,  white  of  egg. 

Fibrin,  globulin, Blood  contained  in  meat. 

Casein, Milk,  cheese. 

Gluten, Grain  of  wheat  and  other  cereals. 

Vegetable  albumin, Soft  growing  vegetables. 

Legumin, Peas,  beans,  lentils,  etc. 

Gelatin, Bones. 

2.  Saccharine  group — non-nitrogenized,  C.  O.  H. 

Cane  sugar,  beet  root  sugar,    .    .     Sugar  cane,  beets,  etc. 

Glucose,  grape  sugar, Fruits. 

Itiosite,  liver  sugar,  glycogen,     .     Muscles,  liver,  etc. 
Lactose  or  milk  sugar,    ....     Milk. 

Starch, Cereals,  tuberous  roots  and  leguminous 

plants. 

3.  Oleaginous  group — non-nitrogenized,  C.  O.  H. 

Animal  fats  and  oils,  .    .    .    .   ~\    Found  in  the  adipose  tissue  of  animals, 

Stearin,  olein, .    .    >•        seeds,  grains,  nuts,  fruits,  and  other 

Palm itin,  fatty  acids,  .    .    .    .   J        vegetable  tissues. 

4.  Inorganic  group.     Water,  sodium  and  potassium  chlorides,  sodium, 
calcium,  magnesium  and  potassium  phosphates,  calcium  carbonate  and  iron. 

5.  Vegetable   acid   group.     Malic,  citric,  tartaric   and  other  acids, 
found  principally  in  fruits. 

6.  Accessory  foods.     Tea,  coffee,  alcohol,  cocoa,  etc. 

The  Albuminous  principles  enter  largely  into  the  composition  of  the 
body,  and  constitute  the  organic  bases  of  the  different  tissues;  they  are 
mainly  required  for  the  growth  and  repair  of  the  tissues.  There  is  good 
reason  to  believe  that  the  albuminous  principles  are  decomposed  in  the 
body  into  fat  and  urea,  and  the  former  when  oxidized  gives  ris'e  to  the 
evolution  of  heat  and  force,  while  the  latter  is  eliminated  by  the  kidneys. 
Muscular  work,  however,  does  not  result  from  a  destruction  of  the  albu- 
minous compounds.  The  oxidation  of  the  carbonaceous  compounds,  sugars 


22  HUMAN  PHYSIOLOGY. 

and  oils,  furnishing  the  force  which  is  transformed  by  the  muscular  system 
into  motor  power.  When  employed  exclusively  as  food  for  any  length  of 
time,  the  albuminous  substances  are  incapable  of  supporting  life. 

The  Saccharine  principles  are  important  to  the  process  of  nutrition,  but 
the  changes  which  they  undergo  are  not  fully  understood ;  they  form  but  a 
small  proportion  of  the  animal  tissues,  and  by  oxidation  generate  heat  and 
force.  Starch  undergoes  conversion  into  dextrin  and  grape  sugar. 

The  Oleaginous  principles  form  a  large  part  of  the  tissues  of  the  body. 
They  are  introduced  into  the  system  as  food,  and  are  formed  also  from  a 
transformation  of  albuminous  matter  during  the  nutritive  process ;  they 
enter  into  the  composition  of  nervous  and  muscular  tissue,  and  are  stored 
up  as  adipose  tissue  in  the  visceral  cavities  and  subcutaneous  connective 
tissue,  thus  giving  roundness  to  the  form  and  preventing,  to  some  extent, 
the  radiation  of  heat.  While  they  aid  in  the  reconstruction  of  tissue,  they 
mainly  undergo  oxidation,  giving  rise  to  the  production  of  heat  and  the 
evolution  of  muscular  and  nervous  force. 

The  Inorganic  principles  constitute  an  essential  part  of  all  animal  tissues, 
and  are  introduced  with  the  food. 

Water  is  present  in  all  fluids  and  solids  of  the  body,  holding  their 
ingredients  in  solution,  promoting  the  absorption  of  new  material  into  the 
blood  and  tissues,  and  the  removal  of  waste  ingredients. 

Sodium  chloride  is  an  essential  constituent  of  all  tissues,  regulating  the 
passage  of  fluids  through  animal  membranes  (endosmosis  and  exosmosis). 

Calcium  phosphate  gives  solidity  to  bones  and  teeth,  constituting  more 
than  one-half  their  substance. 

Iron  is  a  constituent  of  the  coloring  matter  of  the  blood. 

The  Vegetable  acids  are  important  to  nutrition,  and  tend  to  prevent  the 
scorbutic  diathesis. 

The  Accessory  foods  also  influence  the  process  of  nutrition.  Tea  excites 
the  respiratory  function,  increasing  the  elimination  of  carbonic  acid.  Coffee 
is  a  stimulant  to  the  nervous  system ;  increases  the  force  of  the  heart's 
action,  increases  the  arterial  tension  and  retards  waste. 

Alcohol,  when  introduced  into  the  system  in  small  quantities,  undergoes 
oxidation  and  contributes  to  the  production  of  force,  and  is  thus  far  a  food. 
It  excites  the  gastric  glands  to  increased  secretion,  improves  the  digestion, 
accelerates  the  action  of  the  heart  and  stimulates  the  activities  of  the 
nervous*  centres.  In  zymotic  diseases,  and  all  cases  of  depression  of  the 
vital  powers,  it  is  most  useful  as  a  restorative  agent.  When  taken  in 
excessive  quantities,  it  is  eliminated  by  the  lungs  and  kidneys.  The  meta- 
morphosis of  the  tissue  is  retarded,  the  elimination  of  urea  and  carbonic 


FOOD.  23 

acid  is  lessened,  the  temperature  lowered,  the  muscular  powers  impaired 
and  the  resistance  to  depressing  external  influences  diminished.  When 
taken  through  a  long  period  of  time,  alcohol  impairs  digestion,  produces 
gastric  catarrh,  disorders  the  secreting  power  of  the  hepatic  cells.  It  also 
diminishes  the  muscular  power  and  destroys  the  structure  and  composition 
of  the  cells  of  the  brain  and  spinal  cord.  The  connective  tissue  of  the  body 
increases  in  amount,  and  subsequently  contracting,  gives  rise  to  sclerosis. 

A  proper  combination  of  different  alimentary  principles  is  essential 
for  healthy  nutrition ;  no  one  class  being  capable  of  maintaining  life  for 
any  definite  length  of  time. 

The  Albuminous  food  in  excess  promotes  the  arthritic  diathesis,  mani- 
fecting  itself  as  gout,  gravel,  etc. 

The  Oleaginous  food  in  excess  gives  rise  to  the  bilious  diathesis,  while  a 
deficiency  of  it  promotes  the  scrofulous. 

The  Farinaceous  food,  when  long  continued  in  excess,  favors  the  rheu- 
matic diathesis  by  the  development  of  lactic  acid. 

The  Alimentary  Principles  are  not  introduced  into  the  body  as  such, 
but  are  combined  in  proper  proportions  to  form  compound  substances, 
termed  foods,  e.  g.,  bread,  milk,  eggs,  meat,  etc.,  the  nutritive  value  of  each 
depending  upon  the  extent  to  which  these  principles  exist. 

PERCENTAGE  COMPOSITION  OF  DIFFERENT  FOODS. 


Bread, 

WATER. 
77 

ALBUMIN. 
8.1 

STARCH. 

47.4 

SUGAR. 
7.6 

FATS. 

1.6 

SALTS. 
2-3 

Milk, 

86 

4.1 

^  /  *T^ 

o 

C.2 

•3.Q 

0.8 

Eggs, 

•  74 

I4.O 

0 

O  y 

IO.C 

I.e 

Meat,     .    , 
Potatoes,    , 
Corn, 
Oatmeal, 
Turnips, 
Carrots, 
Rice, 

.    ...  54 
...  75 
.    ...  14 
.    ...  15 
.   .   .   .91 
.   .    .   .83 
.  n 

27.6 

2.1 
II.  I 

12.6 
1.2 

i-3 
6.T 

18.8 
64.7 
58-4 

% 

7Q.I 

3-2 

0.4 
5-4 

2.1 

6.1 

0.4 

*  v»  j 

15-45 

0.2 

8.1 
5-6 

0.2 
0.7 

*.j 

2-95 
0.7 

i-7 
6 

I.O 
O.S 

The  amount  of  food  required  in  24  hours  is  estimated  from  the  total 
quantity  of  carbon  and  nitrogen  excreted  from  the  body  in  24  hours;  these 
two  elements  representing  the  waste  or  destruction  of  the  carbonaceous  and 
nitrogenized  compounds.  It  has  been  determined  by  experimentation  that 
about  4600  grains  of  carbon  and  about  300  grains  of  nitrogen  are  elimi- 
nated from  the  body  daily;  the  ratio  being  about  15  to  i.  That  the  body 
may  be  kept  in  its  normal  condition,  a  proper  proportion  of  carbonaceous 
(bread)  to  nitrogenized  (meat)  food  should  be  observed  in  the  diet. 


24  HUMAN   PHYSIOLOGY. 

The  method  of  determining  the  proper  amounts  of  both  kinds  of  food  is 
as  follows : — 

1000  grains  of  bread  (2  oz.)  contain  300  grs.  C.  and  10  grs.  N. 

To  obtain  the  requisite  amount  of  nitrogen  from  bread,  30,000  grains, 
or  about  4  Ibs.,  containing  9000  grains  of  carbon  and  300  of  nitrogen, 
would  have  to  be  consumed.  Under  such  a  diet  there  would  be  a  large 
excess  of  carbon,  which  would  be  undesirable.  On  a  meat  diet  the  reverse 
obtains : — 

1000  grains  of  meat  (2  oz.)  contain  100  grs.  C.  and  30  grs.  N. 

To  obtain  the  requisite  amounts  of  carbon  from  meat,  45,000  grains,  or 
about  6*4  Ibs.,  containing  4500  grains  of  carbon  and  1350  grains  of  nitro- 
gen, would  have  to  be  consumed.  Under  such  circumstances  there  would 
arise  an  excess  of  nitrogen  in  the  system,  which  would  be  equally  undesir- 
able and  injurious.  By  combining  these  two  articles,  however,  in  proper 
proportion,  the  requisite  amounts  of  carbon  and  nitrogen  can  be  obtained 
without  any  excess  of  either,  e.  g.  : — 

2  Ibs.  of  bread  contain  4630  grs.  C.  and  154  grs.  N. 
#"          meat        "          463   "     «     «     154   "     " 


5093  C.  308  N. 

The  amount  of  carbon  and  nitrogen  necessary  to  compensate  for  the  loss 
to  the  system  daily  would  be  contained  in  the  above  amount  of  food.  As 
about  3^  oz.  of  oil  or  butter  are  consumed  daily,  the  quantity  of  bread  can 
be  reduced  to  19  oz.  In  the  quantities  of  bread  and  meat  above  mentioned, 
there  are  4.2  oz.  albumin,  9.3  sugar  and  starch. 


DIGESTION. 

Digestion  is  a  physical  and  chemical  process,  by  which  the  food  intro- 
duced into  the  alimentary  canal  is  liquefied  and  its  nutritive  principles 
transformed  by  the  digestive  fluids  into  new  substances  capable  of  being 
absorbed  into  the  blood. 

The  Digestive  Apparatus  consists  of  the  alimentary  canal  and  its 
appendages,  viz. :  teeth,  salivary,  gastric  and  intestinal  glands,  liver  and 
pancreas. 

Digestion  maybe  divided  into  seven  stages:  prehension,  mastication, 
insalivatioa,  deglutition,  gastric  and  intestinal  digestion  and  defecation. 


DIGESTION.  25 

Prehension,  the  act  of  conveying  food  into  the  mouth,  is  accomplished 
by  the  hands,  lips  and  teeth. 

Mastication  is  the  trituration  of  the  food,  and  is  accomplished  by  the 
teeth  and  lower  jaw,  under  the  influence  of  muscular  contraction.  When 
thoroughly  divided,  the  food  presents  a  greater  surface  for  the  solvent 
action  of  the  digestive  fluids,  thus  aiding  the  general  process  of  digestion. 

The  Teeth  are  thirty-two  in  number,  sixteen  in  each  jaw,  and  divided 
into  four  incisors  or  cutting  teeth,  two  canines,  four  bicuspids,  and  six 
molars  or  grinding  teeth;  each  tooth  consists  of  a  crown  covered  by 
enamel,  a  neck,  and  a  root  surrounded  by  the  crusta  petrosa,  and  imbedded 
in  the  alveolar  process  ;  a  section  through  a  tooth  shows  that  its  substance 
is  made  of  dentine,  in  the  centre  of  which  is  the  pulp  cavity,  containing 
blood  vessels  and  nerves. 

The  lower  jaw  is  capable  of  making  a  downward  and  an  upward,  a 
lateral  and  an  antero-posterior  movement,  dependent  upon  the  construction 
of  the  temporo-maxillary  articulation. 

The  jaw  is  depressed  by  the  contraction  of  the  digastric,  genio-hyoid, 
mylo-hyoid  and  platysma  myoitles  muscles ;  elevated  by  the  temporal, 
masseter  and  internal pterygoid  muscles ;  moved  laterally  by  the  alternate 
contraction  of  the  external  pterygoid  muscles ;  moved  anteriorly  by  the 
Pterygoid  and  posteriorly  by  the  united  actions  of  the  genio-hyoid,  mylo' 
hyoid  and  posterior  fibres  of  the  temporal  muscle. 

The  food  is  kept  between  the  teeth  by  the  intrinsic  and  extrinsic  mus- 
cles of  the  tongue  from  within,  and  the  orbicularis  oris  and  buccinator 
muscles  from  without. 

The  Movements  of  Mastication,  though  originating  in  an  effort  of 
the  will  and  under  its  control,  are,  for  the  most  part,  of  an  automatic  or 
reflex  character,  taking  place  through  the  medulla  oblongata  and  induced 
by  the  presence  of  food  within  the  mouth.  The  nerves  and  nerve  centres 
involved  in  this  mechanism  are  shown  in  the  following  table  : — 

NERVOUS  CIRCLE  OF  MASTICATION. 

AFFERENT   OR   EXCITOR    NERVES.  EFFERENT   OR    MOTOR    NERVES. 

1.  Lingual  branch  of  5th  pair.  I.  3d  branch  of  5th  pair. 

2.  Glosso-pharyngeal.  2.  Hypo-glossal. 

3.  Facial. 

The  impressions  made  upon  the  terminal  filaments  of  the  sensory  nerves 
are  transmitted  to  the  medulla ;  motor  impulses  are  here  generated  which 
C 


26 


HUMAN    PHYSIOLOGY. 


are  transmitted  through  motor  nerves  to  the  muscles  involved  in  the  move- 
ments of  the  lower  jaw.  The  medulla  not  only  generates  motor  impulses, 
but  coordinates  them  in  such  a  manner  that  the  movements  of  mastication 
may  be  directed  toward  the  accomplishment  of  a  definite  purpose. 

Insalivation  is  the  incorporation  of  the  food  with  the  saliva  secreted 
by  the  parotid,  sub-ma xillary  and  sub-lingttal  glands  ;  the  pa rotid  saliva, 
thin  and  watery,  is  poured  into  the  mouth  through  Steno's  duct ;  the  sub- 
maxillary  and  sub- lingual  salivas,  thick  and  viscid,  are  poured  into  the 
mouth  through  Wharton's  and  Bartholini's  ducts. 

In  their  minute  structure  the  salivary  glands  resemble  each  other.  They 
belong  to  the  racemose  variety,  and  consist  of  small  sacs  or  vesicles, 
which  are  the  terminal  expansions  of  the  smallest  salivary  ducts.  Each 
vesicle  or  acinus  consists  of  a  basement  membrane  surrounded  by  blood 


FIG.  i. 


CELLS  OF  THE  ALVEOLI  OF  A  SEROUS  OR  WATERY  SALIVARY  GLAND. 

A.  After  rest.      B.  After  a  short  period  of  activity.      C.  After  a  prolonged  period  of 
activity.— From  Yeo's  Text-Book  of  Physiology. 

vessels  and  lined  with  epithelial  cells.  In  the  parotid  gland  the  lining  cells 
are  granular  and  nucleated ;  in  the  sub-maxillary  and  sub-lingual  glands  the 
cells  are  large,  clear  and  contain  a  quantity  of  mucigen.  During  and  after 
secretion  very  remarkable  changes  take  place  in  the  cells  lining  the  acini, 
which  are  in  some  way  connected  with  the  essential  constituents  of  the 
salivary  fluids. 

In  a  living  serous  gland,  e.  g.,  parotid,  during  rest,  the  secretory  cells 
lining  the  acini  of  the  gland  are  seen  to  be  filled  with  fine  granules,  which 
are  often  so  abundant  as  to  obscure  the  nucleus  and  enlarge  the  cells  until 
the  lumen  of  the  acinus  is  almost  obliterated  (Fig.  i).  When  the  gland 
begins  to  secrete  the  saliva,  the  granules  disappear  from  the  outer  boundary 
of  the  cells  which  then  become  clear  and  distinct.  At  the  end  of  the 
secretory  activity,  the  cells  have  become  free  of  granules,  have  become 
smaller  and  more  distinct  in  outline.  It  would  seem  that  the  granular 


DIGESTION. 


27 


matter  is  formed  in  the  cells  during  the  rest,  and   discharged  into  the  ducts 
during  the  activity  of  the  gland. 

In  the  mucous  glands,  e.g.,  sub-maxillary  and  sub-lingual,  the  changes 
that  occur  in  the  cells  are  somewhat  different  (Fig.  2).  During  the  inter- 
vals of  digestion,  the  cells  lining  the  gland  are  large,  clear  and  highly 
refractive,  and  contain  a  large  quantity  of  mucigen.  After  secretion  has 
taken  place,  the  cells  exhibit  a  marked  change.  The  mucigen  cells  have 
disappeared,  and  in  their  place  are  cells  which  are  small,  dark  and  com- 
posed of  protoplasm.  It  would  appear  that  the  cells,  during  rest,  elabor- 
ate the  mucigen  which  is  discharged  into  the  tubules  during  secretory 
activity,  to  become  part  of  the  secretion. 


FIG.  2. 


SECTION   OF   A   "  MUCOUS  "    GLAND. 

A.     In  a  state  of  rest.     B.     After  it  has  been  for  some  time  actively  secreting. — After 

LM  vdowsky . 

Saliva  is  an  opalescent,  slightly  viscid,  alkaline  fluid,  having  a  specific 
gravity  of  1.005.  Microscopical  examination  reveals  the  presence  of 
salivary  corpuscles  and  epithelial  cells.  Chemically  it  is  composed  of 
water,  proteid  matter,  a  ferment  (ptyalin)  and  inorganic  salts.  The  amount 
secreted  in  24  hours  is  about  2^  Ibs.  Its  function  is  twofold  : — 

1.  Physical. — Softens  and   moistens   the    food,  glues  it   together,  and 
facilitates  swallowing. 

2.  Chemical. — Converts  starch  into  grape  stigar.     This  action  is   due 
to  the  presence  of  the  organic  ferment,  ptyalin.     Ptyalin  is  an  amorphous 
nitrogenized  substance,  which  can  be  precipitated  from  the  saliva  by  calcium 
phosphate.     Its  power  of  converting  starch  into  grape  sugar  is  manifested 
most  decidedly  at  the  temperature   of  the  living  body  and  in  a  slightly 


HUMAN   PHYSIOLOGY. 


alkaline  medium.     The  change  consists  in  the  assumption  of  a  molecule 
of  water. 

Starch.  Water.       Grape  Sugar. 

C6H1005  +  H20  =  C6H1206 


NERVOUS  CIRCLE  OF  INSALIVATION. 

AFFERENT    OR    EXCITOR    NERVES.  EFFERENT    OR    MOTOR    NERVES. 

1.  Lingual  branch  of  5th  pair.  I.  Auriculo-temporal  branch  of  5th 

2.  Glosso-pharyngeal.  pair,  for  parotid  gland. 

2.  Chorda   tympani,    for   sub-maxil- 
lary and  sub  lingual  glands. 

The  centres  regulating  the  secretion  are  two,  viz. :  The  medulla  oblon- 
gata  and  the  submaxillary  ganglion  of  the  sympathetic ;  the  latter  acting 
antagonistically  to  the  former.  Impressions  excited  by  the  food  in  the 
mouth  reach  the  medulla  oblongata  through  the  afferent  nerves ;  motor  im- 
pulses are  there  generated  which  pass  outward  through  the  efferent  nerves. 

Stimulation  of  the  auriculo-temporal  branch  increases  the  flow  of  saliva 
from  the  parotid  gland ;  division  arrests  it. 

Stimulation  of  the  chorda  tympani  is  followed  by  a  dilation  of  the  blood 
vessels  of  the  sub-maxillary  gland,  increased  flow  of  blood  (thus  acting  as 
a  vaso-dilator  nerve)  and  an  abundant  discharge  of  a  thin  saliva ;  division 
of  the  nerve  arrests  the  secretion. 

Stimulation  of  the  cervical  sympathetic  is  followed  by  a  contraction  of 
the  blood  vessels,  diminishing  the  flow  of  blood  (thus  acting  as  a  vase-con- 
strictor nerve)  and  a  diminution  of  the  secretion,  which  now  becomes  thick 
and  viscid ;  division  of  the  sympathetic  does  not,  however,  completely 
dilate  the  vessels.  There  is  evidence  of  the  existence  of  a  local  vaso- 
motor  mechanism,  which  is  inhibited  by  the  chorda  tympani ;  exalted  by 
the  sympathetic. 

Deglutition  is  the  act  of  transferring  food  from  the  mouth  into  the 
stomach,  and  may  be  divided  into  three  stages : — 

1.  The  passage  of  the  bolus  from  the  mouth  into  the  pharynx. 

2.  From  the  pharynx  into  the  oesophagus. 

3.  From  the  oesophagus  into  the  stomach. 

In  the  ist  stage,  which  is  entirely  voluntary,  the  mouth  is  closed  and 
respiration  momentarily  suspended;  the  tongue,  placed  against  the  roof 
of  the  mouth,  arches  upward  and  backward,  and  forces  the  bolus  into  the 
fauces. 

In  the  2d  stage,  which  is  entirely  reflex,  the  palate  is  made  tense  and 
directed  upward  and  backward  by  the  levatores-palati  and  tensores-palati 


DIGESTION.  29 

muscles ;  the  bolus  is  grasped  by  the  superior  constrictor  muscle  of  the 
pharynx  and  rapidly  forced  into  the  oesophagus. 

The  food  is  prevented  from  entering  the  posterior  nares  by  the  uvula 
and  the  closure  of  the  posterior  half-arches  (the  palato  pharyngei  muscles) ; 
from  entering  the  larynx  by  its  ascent  under  the  base  of  the  tongue  and 
the  action  of  the  epiglottis. 

In  the  $d  stage,  the  longitudinal  and  circular  muscular  fibres,  contracting 
from  above  downward,  strip  the  bolus  into  the  stomach.  [For  nervous 
mechanism  of  Deglutition,  see  Medulla  Oblongata.] 

Gastric  Digestion.  The  stomach  is  a  dilation  of  the  alimentary  canal, 
13  inches  long,  5  inches  deep,  having  a  capacity  of  about  5  pints;  there 
can  be  distinguished  a  cardiac  and  pyloric  orifice,  a  greater  and  lesser 
curvature,  a  greater  and  lesser  pouch. 

It  possesses  three  coats  : — 

1 .  Serous,  a  reflection  of  the  peritoneum. 

2.  Muscular,  the  fibres  of  which  are  arranged  longitudinally,  transversely 
and  obliquely. 

3.  Mucous,  thrown  into  folds,  forming  the  rugae. 

Imbedded  in  the  mucous  coat  are  immense  numbers  of  mucous  and 
true  gastric  glands.  In  the  pyloric  end  of  the  stomach  are  found  the 
mucous  glands,  which  are  lined  with  columnar  epithelium  throughout  their 
extent.  In  the  cardiac  end  are  found  the  true  peptic  glands  (Fig.  3),  the 
ducts  of  which  are  also  lined  with  columnar  cells,  while  the  secretory  parts 
are  lined  with  two  distinct  varieties  of  cells.  One  variety  consists  of  small 
spheroidal,  granular  cells,  which  border  the  lumen  of  the  gland,  and  are 
known  as  the  chief  cells ;  the  other  variety  consists  of  large,  oval,  well- 
defined  granular  cells,  much  less  abundant,  and  are  situated  between  the 
basement  membrane  of  the  gland  and  the  'chief  cells.  From  their  position 
they  have  been  termed  parietal  cells.  During  the  intervals  of  digestion  the 
chief  cells  are  pale,  and  the  hyaline  substance  of  which  they  are  composed 
is  finely  granular.  During  the  stage  of  active  secretion  the  cells  become 
swollen  and  turbid,  and  are  then  said  to  be  rich  in  pepsin.  Toward  the 
end  of  digestion  the  granules  disappear,  the  cells  become  pale  and  return  to 
their  former  size. 

During  the  intervals  of  digestion,  the  mucous  membrane  of  the  stomach 
is  pale  and  covered  with  a  layer  of  mucus.  Upon  the  introduction  of  food, 
the  blood  vessels  dilate  and  become  filled  with  blood,  and  the  mucous 
membrane  becomes  red.  At  the  same  time  small  drops  of  a  fluid,  the 
gastric  juice,  begin  to  exude  upon  its  surface,  which  gradually  run  together 
and  trickle  down  the  sides  of  the  stomach. 


30 


HUMAN   PHYSIOLOGY. 


The  secretion  of  gastric  juice  is  a  reflex  act,  taking  place  through  the 
central  nervous  system  and  called  forth  in  response  to  the  stimulus  of  food 
in  the  stomach.  That  the  central  nervous  system  also  directly  influences 
the  production  of  the  secretion  is  shown  by  the  fact  that  mental  emotion, 
such  as  fear  and  anger,  will  arrest  or  vitiate  the  normal  secretion.  The 
reflex  nature  of  the  process  can  be  shown  by  experimentation  upon  the 
pneumogastric  nerve.  If  during  digestion,  when  the  peristaltic  movements 


FIG.  3. 


Diagram  showing  the  relation  of  the  ultimate  twigs  of  the  blood  vessels,  V  and  A,  and 
of  the  absorbent  radicles  to  the  glands  of  the  stomach  and  the  different  kinds  of  epi- 
thelium, viz.,  above  cylindrical  cells:  small,  pale  cells  in  the  lumen,  outside  which 
are  the  dark  ovoid  cells. — From  Yea's  Text-Book  of  Physiology. 

are  active  and  the  gastric  mucous  membrane  flushed  and  covered  with 
gastric  juice,  the  pneumogastric  nerves  are  divided  on  both  sides,  the 
mucous  membrane  becomes  pale,  the  secretion  is  arrested  and  the  peristaltic 
movements  become  less  marked.  Stimulation  of  the  peripheral  end  produces 
no  constant  effects;  stimulation  of  the  central  end,  however,  is  at  once 
followed  by  dilatation  of  the  vessels,  flushing  of  the  mucous  membrane  and 
a  re-establishment  of  the  secretion.  It  is  evident,  therefore,  that  during 


DIGESTION.  31 

digestion  afferent  impulses  are  passing  up  the  pneumogastrics  to  the  medulla ; 
efferent  impulses,  in  all  probability,  pass  through  the  fibres  of  the  sym- 
pathetic nervous  system  to  the  blood  vessels  and  glands  concerned  in  the 
elaboration  of  the  gastric  juice.  After  all  the  nervous  connections  of  the 
stomach  are  divided,  a  small  quantity  of  juice  continues  to  be  secreted  for 
several  days.  This  has  been  attributed  to  the  action  of  a  local  nervous 
mechanism  and  to  the  direct  action  of  the  food  upon  the  protoplasm  of  the 
secreting  cells. 

The  Gastric  Juice  is  a  secretion  of  the  true  peptic  glands,  and  when 
obtained  from  the  stomach  through  a  fistulous  opening,  is  a  clear,  straw- 
colored  fluid,  decidedly  acid,  with  a  specific  gravity  of  1.005  to  i.oio. 

COMPOSITION  OF  GASTRIC  JUICE. 

Water, 975-°° 

Pepsin, 15.00 

Hydrochloric  acid, 4.78 

Inorganic  salts, , 5-22 


1000.00 

The  water  forms  the  largest  part  of  the  fluid,  and  holds  in  solution  the 
other  ingredients.  It  results  from  a  transudation  from  the  blood  vessels 
under  the  increased  blood  supply.  Of  the  inorganic  salts  the  chlorides  of 
sodium -and  potassium  are  the  most  abundant. 

Pepsin  is  the  organic  nitrogenized  ferment  of  the  gastric  juice,  and  is 
formed,  during  the  intervals  of  digestion,  by  the  peptic  cells.  In  the 
presence  of  a  small  per  cent,  of  an  acid,  it  acquires  the  property  of  con- 
verting the  albumin  of  the  food  into  albuminose  or  peptones. 

Hydrochloric  acid  is  present  in  small  quantity,  and  gives  the  juice  its 
acidity.  In  all  probability,  its  production  is  due  to  the  activity  of  the 
parietal  cells.  These  two  characteristic  ingredients  of  the  gastric  juice 
exist  in  a  state  of  combination  as  hydrochloro-peptic  acid,  and  the  presence 
of  both  is  absolutely  essential  for  the  complete  digestion  of  the  food. 

When  the  food  enters  the  stomach,  it  is  subjected  to  the  peristaltic  action 
of  the  muscular  coat,  and  thoroughly  incorporated  with  the  gastric  juice. 
This  fluid  has  a  twofold  action  upon  the  food: — 1st.  A  physical  action,  by 
which  the  fibrous  tissues  of  meats,  the  cellulose  and  hard  parts  of  grains 
and  vegetables,  are  dissolved  away  until  the  food  is  disintegrated  and 
reduced  to  the  liquid  condition.  2d.  A  chemical  action,  by  which  the 
albuminous  principles  are  transformed  into  peptones.  The  more  important 
foods  with  their  contained  albuminous  principles  are  shown  on  page  21. 


32  HUMAN   PHYSIOLOGY. 

Upon  meat  the  gastric  juice  has  a  decidedly  disintegrating  action.  The 
connective  tissue  is  first  dissolved,  the  fibres  are  separated,  the  sarcolemma 
softened,  and  the  whole  reduced  to  a  grumous,  pultaceous  mass.  Milk 
undergoes  coagulation  in  from  ten  to  fifteen  minutes,  the  casein  being 
precipitated  in  the  form  of  soft  flocculi,  which  are  easy  of  transformation 
into  peptone.  Upon  Vegetable  tissues,  the  gastric  juice  exerts  also  a  dis- 
integrating action;  the  cellulose  and  woody  fibres  are  dissolved  and  the 
nutritive  principles  liberated.  Bread  undergoes  liquefaction  quite  readily. 

The  Principal  Action  of  the  gastric  juice,  however,  is  to  transform  the 
different  albuminous  principles  of  the  food  into  peptones  or  albuminose,  the 
different  stages  of  which  are  due  to  the  acid  and  pepsin  respectively.  When 
freed  from  its  combination,  the  hydrochloric  acid  converts  the  albumin 
into  acid  albtimin  or  parapcptone  ;  while  this  intermediate  product  is  being 
formed,  the  pepsin  converts  it  at  once  into  peptone.  In  order  that  the 
digestion  of  albumin  may  be  complete,  it  is  necessary  that  both  the  acid 
and  pepsin  be  present  in  proper  quantity.  Before  digestion,  the  albuminous 
principles  are  insoluble  in  water  and  incapable  of  being  absorbed.  After 
digestion,  they  become  soluble  and  are  readily  absorbed.  Peptones  differ 
from  the  albumins  in  being — 

1.  Diffusible ',  passing  rapidly  through  the  mucous  membrane  and  walls 
of  the  blood  vessels. 

2.  Non-coagulable  by  heat,  nitric  or  acetic  acids;  but  are  readily  precipi- 
tated by  tannic  acid. 

3.  Soluble  in  water  and  saline  solutions. 

4.  Assimilable  by  the  blood  ;  when  injected  into  it,  they  do  not  reappear 
in  the  urine. 

Gastric  juice  exerts  no  influence  either  upon  grape  sugar,  cane  sugar, 
starch  or  fat. 

Gastric  Digestion  occupies  on  the  average  from  3  to  5  hours,  but 
varies  in  duration  according  to  the  nature  and  quantity  of  the  food,  exercise, 
temperature,  etc. 

The  Amount  of  gastric  juice  secreted  in  24  hours  varies,  under  normal 
conditions,  from  8  to  14  pounds. 

Movements  of  the  Stomach.  As  soon  as  digestion  commences,  the 
cardiac  and  pyloric  orifices  are  closed ;  the  walls  of  the  stomach  contract 
upon  the  food,  and  a  peristaltic  action  begins,  which  carries  the  food  along 
the  greater  and  lesser  curvatures,  and  thoroughly  incorporates  it  with  the 
gastric  juice.  As  soon  as  any  portion  of  the  food  is  digested,  it  passes 
through  the  pylorus  into  the  intestine. 


DIGESTION.  33 

TABLE  SHOWING  DIGESTIBILITY  OF  VARIOUS  ARTICLES 
OF  FOOD. 

HOURS.      MINUTES. 

Eggs,  whipped, I  20 

"      soft  boiled, 3 

"      hard  boiled, 3  30 

Oysters,  raw, 2  55 

"     stewed, 3  30 

Lamb,  broiled, .2  30 

Veal,  broiled, 4 

Pork,  roasted, 5  15 

Beefsteak,  broiled, 3 

Turkey,  roasted, 2  25 

Chicken,  boiled, 4 

"      fricasseed, 2  45 

Duck,  roasted, 4 

Soup,  barley,  boiled, I  30 

«      beans,       " 3 

"      chicken,   " 3 

"      mutton,     "         3  30 

Liver,  beef,  broiled, 2 

Sausage,  "  3  20 

Green  corn,  boiled, 3  45 

Beans,  "       2  30 

Potatoes,  roasted, 2  30 

"  boiled, 3  30 

Cabbage,      "        4  30 

Turnips,       "        3  30 

Beets,  «       3  45 

Parsnips,      " 2  30 

Vomiting.  The  act  of  vomiting  is  usually  preceded  by  nausea  and  a 
discharge  of  saliva  into  the  mouth.  This  is  then  swallowed,  and  carries 
into  the  stomach  a  quantity  of  air  which  facilitates  the  ejection  of  the  con- 
tents of  the  stomach  by  aiding  the  relaxation  of  the  cardiac  sphincter.  A 
deep  inspiration  is  then  taken,  during  which  the  lower  ribs  are  drawn  in 
and  the  diaphragm  descends  and  remains  contracted.  At  the  same  time 
the  glottis  is  closed.  A  sudden  expiratory  effort  is  now  made,  and  the  cardiac 
orifice  being  open,  the  abdominal  muscles  contracting,  press  upon  the 
stomach  and  forcibly  eject  its  contents  into  the  mouth. 

Intestinal  Digestion.  The  intestine  is  about  20  feet  long,  \yz  inches 
in  diameter,  and  possesses  three  coats  : — 

1.  Serous  (peritoneal). 

2.  Muscular,  the  fibres  of  which  are  arranged  longitudinally  and  trans- 
versely. 

3.  Mucous,  thrown  into  folds,  forming  the  valvuhe  connivences. 


34 


HUMAN   PHYSIOLOGY. 


This  stage  of  digestion  is  probably  the  most  complex  and  important ;  here 
the  different  alimentary  principles  are  further  elaborated  and  prepared  for 
absorption  into  the  blood  by  being  acted  upon  by  the  intestinal  juice,  pan- 
creatic juice  and  bile. 

Throughout  the  mucous  coat  are  imbedded  the  intestinal  follicles,  the 
glands  of  Brunner  and  Lieberkiihn.  They  secrete  the  true  intestinal  juice , 
which  is  an  alkaline,  viscid  fluid,  composed  of  water,  organic  matter  and 
salts.  \\s>  function  is  to  convert  starch  into  glucose,  and  assist  in  the  diges- 
tion of  the  albuminoids. 

The  Pancreatic  Juice  is  secreted  by  the  pancreas,  a  flattened  gland 
about  six  inches  long,  running  transversely  across  the  posterior  wall  of  the 
abdomen,  behind  the  stomach ;  its  duct  opens  into  the  duodenum. 

FIG.  4. 


ONE   SACCULE   OF   THE    PANCREAS    OF   THE    RABBIT    IN    DIFFERENT  STATES   OF  ACTIVITY. 

A  After  a  period  of  rest,  in  which  case  the  outlines  of  the  cells  are  indistinct,  and  the 
inner  zone,  i.  e.,  the  part  of  the  cells  (a)  next  the  lumen  (c),  is  broad  and  filled  with 
fine  granules.  B.  After  the  gland  has  poured  out  its  secretion,  when  the  cell  out- 
lines (d)  are  clearer,  the  granular  zone  (a)  is  smaller,  and  the  clear  outer  zone  is  wider. 
—From  Yto's  Text-Book  of  Physiology,  after  Kiihne  and  Lea. 

The  pancreas  is  similar  in  structure  to  the  salivary  glands,  consisting  ot 
a  system  of  ducts  terminating  in  acini.  The  acini  are  tubular  or  flask- 
shaped,  and  consist  of  a  basement  membrane  lined  by  a  layer  of  cylindrical, 
conical  cells,  which  encroach  upon  the  lumen  of  the  acini.  The  cells 
exhibit  a  difference  in  their  structure  (Fig.  4),  and  may  be  said  to  consist 
of  two  zones,  viz.,  an  oziter  parietal  zone,  which  is  transparent  and  appar- 
ently homogeneous,  staining  Vapidly  with  carmine;  an  inner  zone,  which 
borders  the  lumen,  and  is  distinctly  granular  and  stains  but  slightly  with 
carmine.  These  cells  undergo  changes  similar  to  those  exhibited  by  the 
cells  of  the  salivary  glands  during  and  after  active  secretion.  As  soon  as 


DIGESTION.  35 

the  secretory  activity  of  the  pancreas  is  established,  the  granules  disappear, 
and  the  inner  granular  layer  becomes  reduced  to  a  very  narrow  border 
while  the  outer  zone  increases  in  size  and  occupies  nearly  the  entire  cell. 
During  the  intervals  of  secretion,  however,  the  granular  layer  reappears 
and  increases  in  size  until  the  outer  zone  is  reduced  to  a  minimum.  It 
would  seem  that  the  granular  matter  is  formed  by  the  nutritive  processes 
occurring  in  the  gland  during  rest,  and  is  discharged  during  secretory 
activity  into  the  ducts  and  takes  part  in  the  formation  of  the  pancreatic 
secretion. 

The  pancreatic  juice  is  transparent,  colorless,  strongly  alkaline  and  viscid, 
and  has  a  specific  gravity  of  1.040.  It  is  one  of  the  most  important  of  the 
digestive  fluids,  as  it  exerts  a  transforming  influence  upon  all  the  classes  of 
alimentary  principles,  and  has  been  shown  to  contain  at  least  three  distinct 
ferments.  It  has  the  following  composition  : — 

COMPOSITION  OF  PANCREATIC  JUICE. 

Water, 900.76 

Albuminoid  substances, 90.44 

Inorganic  salts, 8.80 


100000 

The  pancreatic  juice  is  characterized  by  its  action  :  ist.  Upon  starch. 
When  starch  is  subjected  to  the  action  of  the  juice,  it  is  at  once  transformed 
into  glucose;  the  change  takes  place  more  rapidly  than  when  saliva  is 
added.  This  action  is  caused  by  the  presence  of  a  special  ferment,  amyl- 
opsin.  2d.  Upon  albumin.  The  albuminous  bodies  are  changed  by  the 
juice  into,  first,  an  alkali  albumin,  and  then  into  peptone.  The  albumin 
does  not  swell  up,  as  is  the  case  in  gastric  digestion,  but  is  gradually  cor- 
roded and  dissolved.  This  change  is  due  to  the  presence  of  the  ferment, 
trypsin.  Long-continued  action  of  trypsin  converts  the  peptones  into  two 
crystalline  bodies,  leucine  and  tyrosin.  3d.  Upon  fats.  The  most  striking 
action  of  the  pancreatic  juice  is  the  etnulsification  of  the  fats  or  their  sub- 
division into  minute  particles  of  microscopic  size.  This  change  takes  place 
rapidly  and  depends  upon  the  alkalinity  of  the  fluid  and  the  quantity  of 
albumin  present,  combined  with  the  intestinal  movements.  The  neutral 
fats  are  also  decomposed  into  their  cor  responding  fatty  acids  and  glycerine  ; 
the  acids  thus  set  free  unite  with  the  alkaline  bases  present  in  the  intestine 
and  form  soaps.  This  decomposition  of  the  neutral  fats  is  caused  by  the 
ferment,  steapsin.  4th.  Upon  cane  sugar  the  juice  also  exerts  a  special 
influence,  converting  it  readily  into  glucose. 


36  HUMAN   PHYSIOLOGY. 

The  total  quantity  of  this  fluid  secreted  in  twenty-four  hours  has  not 
been  accurately  determined  ;  it  varies  from  one  to  two  pounds  ;  it  is  poured 
out  most  abundantly  an  hour  after  meals. 

The  Bile  has  an  important  influence  in  the  elaboration  of  the  food  and 
its  preparation  for  absorption.  It  is  a  golden-brown,  viscid  fluid,  having  a 
neutral  or  alkaline  reaction  and  a  specific  gravity  of  1.020. 

COMPOSITION  OF  BILE. 

Water, 859.2 

Sodium  glycocholate,    ^ 

Sodium  taurocholate,    j 9I-4 

Fat, 9.2 

Cholesterine, 2.6 

Mucus  and  coloring  matter, 29.8 

Salts, 7.8 


1000.00 

The  Biliary  salts,  sodium  glycocholate  and  taurocholate,  are  character- 
istic ingredients,  and  are  formed  in  the  liver  by  the  process  of  secretion, 
from  materials  furnished  by  the  blood.  It  is  probable  that  they  are  derived 
from  the  nitrogenized  compounds,  though  the  stages  in  the  process  are 
unknown.  They  are  reabsorbed  from  the  small  intestine  to  play  some 
ulterior  part  in  nutrition. 

Cholesterine  is  a  product  of  waste  taken  up  by  the  blood  from  the  nervous 
tissues  and  excreted  by  the  liver.  It  crystallizes  in  the  form  of  rhombic 
plates,  which  are  quite  transparent.  When  retained  within  the  blood,  it 
gives  rise  to  the  condition  of  cholesterczmia,  attended  with  severe  nervous 
symptoms.  It  is  given  off  in  the  feces  under  the  form  of  stercorine. 

The  Coloring  matters  which  give  the  tints  to  the  bile  are  biliverdin  and 
bilirubiny  and  are  probably  derived  from  the  coloring  matter  of  the  blood. 
Their  presence  in  any  fluid  can  be  recognized  by  adding  to  it  nitric  acid 
containing  nitrous  acid,  when  a  play  of  colors  is  observed,  beginning  with 
green,  blue,  violet,  red  and  yellow. 

The  Bile  is  both  a  secretion  and  an  excretion ;  it  is  constantly  being 
formed  and  discharged  by  the  hepatic  ducts  into  the  gall  bladder,  in  which 
it  is  stored  up,  during  the  intervals  of  digestion.  As  soon  as  food  enters 
the  intestines,  it  is  poured  out  abundantly,  by  the  contraction  of  the  walls 
of  the  gall  bladder. 

The  Amount  secreted  in  24  hours  is  about  2^  pounds. 

Functions  of  the  Bile,  (i)  It  assists  in  the  emulsifi cation  of  the  fats 
and  promotes  their  absorption.  (2)  It  tends  to  prevent  putrefactive  changes 


ABSORPTION.  37 

in  the  food.  (3)  It  stimulates  the  secretions  of  the  intestinal  glands,  and 
excites  the  normal  peristaltic  movement  of  the  bowels. 

The  digested  food,  the  chyme,  is  a  grayish,  pultaceous  mass,  but  as  it 
passes  through  the  intestines  it  becomes  yellow,  from  admixture  with  the 
bile.  It  is  propelled  onward  by  vermicular  motion;  by  the  contraction  of 
the  circular  and  longitudinal  muscular  fibres. 

As  the  digested  food  passes  through  the  intestines,  the  nutritious  mat- 
ters are  absorbed  into  the  blood,  and  the  residue  enters  the  large  intestine. 

The  Faeces  consist  chiefly  of  indigestible  matters,  excretin,  slercorin 
and  salts ;  varying  in  amount  from  4  to  7  ozs.  in  24  hours. 

Defecation  is  the  voluntary  act  of  extruding  the  faeces  from  the  body; 
accomplished  by  a  relaxation  of  the  sphincter  muscle,  the  contraction  of  the 
walls  of  the  rectum,  assisted  by  the  abdominal  muscles. 

The  Gases  contained  in  the  stomach  and  small  intestine  are  oxygen, 
nitrogen,  hydrogen  and  carbonic  acid.  In  the  large  intestine,  carbonic 
acid,  sulphuretted  and  carburetted  hydrogen.  They  are  introduced  with 
the  food,  and  also  developed  by  chemical  changes  in  the  alimentary  canal. 
They  distend  the  intestines,  aid  capillary  circulation,  and  tend  to  prevent 
pressure. 


ABSORPTION. 

The  term  absorption  is  applied  to  the  passage  or  transference  of  material 
into  the  blood  from  the  tissues,  from  the  serous  cavities,  and  from  the 
mucous  surfaces  of  the  body.  The  most  important  of  these  surfaces,  espe- 
cially in  its  relation  to  the  formation  of  the  blood,  is  the  mucous  surface  of 
the  alimentary  canal ;  for  it  is  from  this  organ  that  new  materials  are  de- 
rived which  maintain  the  quality  and  quantity  of  the  blood.  The  absorp- 
tion of  materials  from  the  interstices  of  the  tissues  is  to  be  regarded  rather 
as  a  return  to  the  blood  of  liquid  nutritive  material  which  has  escaped  from 
the  blood  vessels  for  nutritive  purposes,  and  which,  if  not  returned,  would 
lead  to  an  accumulation  of  such  fluid  and  the  development  of  dropsical 
conditions. 

The  anatomical  mechanisms  involved  in  the  absorptive  process  are 
primarily,  the  lymph  spaces,  the  lymph  capillaries  and  blood  capillaries  ; 
secondarily,  the  lymphatic  vessels  and  larger  blood  vessels. 

Lymph  spaces,  Lymph  capillaries,  Blood  capillaries.  Every- 
where throughout  the  body,  in  the  intervals  of  connective  tissue  bundles,  and 
in  the  interstices  of  the  several  structures  of  which  an  organ  is  composed, 


38  HUMAN   PHYSIOLOGY. 

are  found  spaces  of  irregular  shape  and  size,  determined  largely  by  the  nature 
of  the  organ  in  which  they  are  found,  which  have  been  termed  lymph  spaces 
or  lacuna,  from  the  fact  that  during  the  living  condition  they  are  continu- 
ally receiving  the  lymph  which  has  escaped  from  the  blood  vessels  through- 
out the  body.  In  addition  to  the  connective  tissue  lymph  spaces,  various 
observers  have  described  special  lymph  spaces  in  the  testicle,  kidney,  liver, 
thymus  gland,  and  spleen;  in  all  secreting  glands  between  the  basement 
membrane  and  blood  vessels;  around  blood  vessels  (perivascular  spaces) 
and  around  nerves.  The  serous  cavities  01  the  body,  peritoneal,  pleura], 
pericardial,  etc.,  may  also  be  regarded  as  lymph  spaces,  which  are  in  direct 
communication  by  open  mouths  or  stomata  with  the  lymphatic  capillaries. 
This  method  of  communication  is  not  only  true  of  serous  membranes,  but 
to  some  extent  also  of  mucous  membranes.  The  cylindrical  sheaths  and 
endothelial  cells  surrounding  the  brain,  spinal  cord  and  nerves,  can  also  be 
looked  upon  as  lymph  spaces  in  connection  with  lymph  capillaries. 

The  lymphatic  capillaries,  in  which  the  lymphatic  vessels  proper  take 
their  origin,  are  arranged  in  the  form  of  plexuses  of  quite  irregular  shape. 
In  most  situations  they  are  intimately  interwoven  with  the  blood  vessels, 
from  which,  however,  they  can  be  readily  distinguished  by  their  larger 
calibre  and  irregular  expansions.  The  wall  of  the  lymph  capillary  is 
formed  by  a  single  layer  of  epithelioid  cells,  with  sinuous  outlines,  and 
which  accurately  dove'tail  with  each  other.  In  no  instance  are  valves 
found.  In  the  villus  of  the  small  intestine  the  beginning  of  the  lacteal  is 
to  be  regarded  as  a  lymph  capillary,  generally  club-shaped,  which  at  the 
base  of  the  villus  enters  a  true  lymphatic ;  at  this  point  a  valve  is  present, 
which  prevents  regurgitation.  The  lymphatic  capillaries  anastomose  freely 
with  each  other,  and  communicate  on  the  one  hand  with  the  lymph  spaces, 
and  on  the  other  with  the  lymphatic  vessels  proper. 

As  the  shape,  size,  etc.,  of  both  lymph  spaces  and  capillaries  are  deter- 
mined largely  by  the  nature  of  the  tissues  in  which  they  are  contained,  it  is 
not  always  possible  to  separate  the  one  from  the  other.  Their  function, 
however,  may  be  regarded  as  similar,  viz : — the  collection  of  the  lymph 
which  has  escaped  from  the  blood  vessels,  and  its  transmission  onward  into 
the  regular  lymphatic  vessels. 

*  The  blood  capillaries  not  only  permit  the  escape  of  the  liquid  nutritive 
portions  of  the  blood  through  their  delicate  walls,  but  are  also  engaged  in 
the  reabsorption  of  this  transudate  as  well  as  in  the  absorption  of  hew 
materials  from  the  alimentary  canal.  The  extensive  capillary  network 
which  is  formed  by  the  ultimate  subdivision  of  the  arterioles  in  the  sub- 
mucous  tissue  and  villi  of  the  small  intestine  forms  an  anatomical  arrange- 


ABSORPTION.  39 

raent  well  adapted  for  absorption.  It  is  now  well  known  that  in  the 
absorption  of  the  products  of  digestion  the  blood  capillaries  are  more  active 
than  the  lymphatic  capillaries. 

Lymphatic  Vessels.  The  lymphatic  vessels  constitute  a  system  of 
minute,  delicate, transparent  vessels,  found  in  nearly  all  the  organs  and  tissues 
of  the  body.  Having  their  origin  at  the  periphery  in  the  lymphatic  capil- 
laries and  spaces,  they  gradually  converge  toward  the  trunk  of  the  body  and 
empty  into  the  thoracic  duct.  In  their  course  they  pass  through  numerous 
small  ovoid  bodies,  the  lymphatic  glands. 

The  lymphatic  vessels  of  the  small  intestine  (M<?  lacteah]  arise  within 
the  villous  processes  which  project  from  the  inner  surface  of  the  intestine 
throughout  its  entire  extent.  The  wall  of  the  villus  is  formed  by  an  eleva- 
tion of  the  basement  membrane,  and  covered  by  a  layer  of  columnar  epi- 
thelial cells.  The  basis  of  the  villus  consists  of  adenoid  tissue,  fine  plexus 
of  blood  vessels,  unstriped  muscular  fibres  and  the  lacteal  vessel.  The 
adenoid  tissue  consists  of  a  number  of  intercommunicating  spaces,  con- 
taining leucocytes.  The  lacteal  vessel  possesses  a  thin,  but  distinct  wall, 
composed  of  endothelial  plates,  with  here  and  there  openings,  which  bring 
the  interior  of  the  villus  into  communication  with  the  spaces  of  the  adenoid 
tissue. 

The  structure  of  the  larger  vessels  resembles  that  of  the  veins,  consisting 
of  three  coats. — 

i.  External,  composed  of  fibrous  tissue  and  muscular  fibres,  arranged 
longitudinally.  2.  Middle,  consisting  of  white  fibrous  and  yellow  elastic 
tissue,  non-striated  muscular  fibres,  arranged  transversely.  3.  Internal, 
composed  of  an  elastic  membrane,  lined  by  endothelial  cells. 

Throughout  their  course  are  found  numerous  semilunar  valves,  looking 
toward  the  larger  vessels,  formed  by  a  folding  of  the  inner  coat  and 
strengthened  by  connective  tissue. 

Lymphatic  Glands.  The  lymphatic  glands  consist  of  an  external 
capsule  composed  of  fibrous  tissue  which  contains  non-striped  muscular 
fibres :  from  its  inner  surface  septa  of  fibrous  tissue  pass  inward  and  sub- 
divide the  gland  substance  into  a  series  of  compartments  which  communi- 
cate with  each  other.  The  blood  vessels  which  penetrate  the  gland  aru 
surrounded  by  fine  threads,  forming  a  follicular  arrangement,  the  meshes  of 
which  contain  numerous  lymph  corpuscles.  Between  the  follicular  threads 
and  the  wall  of  the  gland  lies  a  lymph  channel  traversed  by  a  reticulum  of 
adenoid  tissue.  The  lymphatic  vessels  after  penetrating  this  capsule  pour 
their  lymph  into  this  channel,  through  which  it  passes ;  it  is  then  collected 


40 


HUMAN    PHYSIOLOGY. 


FIG.  5. 


DIAGRAM    SHOWING  THE   COURSE   OF   THE   MAIN    TRUNKS   OF   THE   ABSORBENT   SYSTEM. 

The  lymphatics  of  lower  extremities  (D)  meet  the  lacteals  of  intestines  (LAC)  at  the 
receptaculum  chyli  (R  C),  where  the  thoracic  duct  begins.  The  superficial  vessels 
are  shown  in  the  diagram  on  the  right  arm  and  leg  (S),  and  the  deeper  ones  on  the 
arm  to  the  left  (D).  The  glands  are  here  and  there  shown  in  groups.  The  small 
right  duct  opens  into  the  veins  on  the  right  side.  The  thoracic  duct  opens  into  the 
union  of  the  great  veins  of  the  left  side  of  the  neck  (T). — Front  Yeo's  Text-Book  of 
Physiology . 


ABSORPTION.  41 

by  the  efferent  vessels  and  transmitted  onward.  The  lymph  corpuscles 
which  are  washed  out  of  the  gland  into  the  lymph  stream  are  formed,  most 
probably,  by  division  of  pre-existing  cells. 

The  Thoracic  Duct  is  the  general  trunk  of  the  lymphatic  system,  into 
which  the  vessels  of  the  lower  extremities,  of  the  abdominal  organs,  of  the 
left  side  of  the  head  and  left  arm  empty  their  contents.  It  is  about  twenty 
inches  in  length,  arises  in  the  abdomen,  opposite  the  third  lumbar  vertebra, 
by  a  dilatation,  \ho.  receptaculum  chyli ;  ascends  along  the  vertebral  column 
to  the  seventh  cervical  vertebra,  and  terminates  in  the  venous  system  at 
the  junction  of  the  internal  jugular  and  subclavian  veins  on  the  left  side. 
The  lymphatics  of  the  right  side  of  the  head,  of  the  right  arm  and  the  right 
side  of  the  thorax,  terminate  in  the  right  thoracic  duct,  about  one  inch  in 
length,  which  joins  the  venous  system  at  the  junction  of  the  internal  jugular 
and  subclavian  on  the  right  side. 

The  general  arrangement  of  the  lymphatic  vessels  is  shown  in  Fig.  5. 

The  Blood  Vessels  which  are  concerned  in  the  conduction  of  fresh 
nutritive  material  from  the  alimentary  canal,  have  their  origin  in  the  elaborate 
capillary  network  in  the  mucous  membrane.  The  small  veins  which  emerge 
from  this  network  gradually  unite,  forming  larger  and  larger  trunks  which 
are  known  as  the  gastric,  superior  and  inferior  mesenteric  veins.  These 
finally  unite  to  form  the  portal  vein,  a  short  trunk  about  three  inches  in 
length.  The  portal  vein  enters  the  liver  at  the  transverse  fissure,  after 
which  it  forms  a  fine  capillary  plexus  ramifying  throughout  the  substance 
of  the  liver;  from  this  plexus  the  hepatic  veins  take  their  origin,  which 
finally  empty  the  blood  into  the  vena  cava  inferior.  (See  Fig.  6.) 

Absorption  of  Food.  Physiological  experiments  have  demonstrated 
that  the  agents  concerned  in  the  absorption  of  new  materials  from  the  ali- 
mentary canal  are: — ist.  The  blood  vessels  of  the  entire  canal,  but  more 
particularly  those  uniting  to  form  the  portal  vein.  2d.  The  lymphatics 
coming  from  the  small  intestine  which  converge  to  empty  into  the  thoracic 
duct.  As  a  result  of  the  action  of  the  digestive  fluids  upon  the  different 
classes  of  food  stuffs,  albumins,  sugars,  starches  and  fats,  there  are  formed, 
peptones,  glucose  and  fatty  emulsion,  which  differ  from  the  former,  in  being 
highly  diffusible,  a  condition  essential  to  their  absorption.  In  order  that 
these  substances  may  get  into  the  blood,  they  must  pass  through  the  layer  of 
cylindrical  epithelial  cells  and  the  underlying  basement  membrane  and  into 
the  lymph  spaces  of  the  villi  and  sub-mucous  tissue.  The  mechanism  by 
which  the  cells  effect  this  passage  of  the  food  is  but  imperfectly  understood. 
D 


42 


HUMAN   PHYSIOLOGY. 


Osmosis  and  filtration  are  conditions,  however,  made  use  of  by  the  cells  in 
the  absorptive  process. 

The  Products  of  digestion  find  their  way  into  the  general  circulation  by 
two  routes  :  — 

I.  The  water  •,  peptones,  glucose  and  soluble  sails,  after  passing  into  the 
lymph  spaces  of  the  villi,  pass  through  the  wall  of  the  capillary  blood  vessel  ; 
entering  the  blood,  they  are  carried  to  the  liver  by  the  vessels  uniting  to 


FIG.  6. 


Diagram  of  the  portal  vein  (/&)  arising  in  the  alimentary  tract  and  spleen  (s),  and  car- 
rying the  blood  from  these  organs  to  the  liver. — From  Yea's  Text-Book  of  P/q 


°hysiology. 


form  the  portal  vein ;  emerging  from  the  liver,  they  are  emptied  into  the 
inferior  vena  cava  by  the  hepatic  vein. 

2.  The  emulsified  fat  enters  the  lymph  capillary  in  the  interior  of  the 
villus;  by  the  contraction  of  the  layer  of  muscular  fibres  surrounding  it 
its  contents  are  forced  onward  into  the  lymphatic  vessel  or  lacteal ;  thence 


ABSORPTION.  43 

into  the  thoracic  duct,  and  finally  into  the  circulation  at  the  junction  of  the 
internal  jugular  and  subclavian  veins  on  the  left  side. 

Absorption  of  Lymph.  Similar  to  the  absorption  of  food  from  the 
alimentary  canal,  is  the  absorption  of  lymph  from  the  lymph  spaces  of  the 
organs  and  tissues.  During  the  passage  of  the  blood  through  the  capillary 
blood  vessels,  a  portion  of  the  liquor  sanguinis  or  plasma  or  lymph,  passes 
through  the  capillary  wall  out  into  the  lymph  spaces.  The  tissue  cells  are 
thus  bathed  with  this  new  material ;  from  it  those  substances  are  selected 
which  are  necessary  for  their  growth,  repair,  and  all  purposes  of  nutrition. 
An  excess  of  nutritive  material,  far  beyond  the  needs  of  the  tissues,  transudes 
from  the  blood  vessels,  and  it  is  this  excess  which  is  absorbed  by  the  lym- 
phatics, and  returned  to  the  blood  by  the  thoracic  duct.  It  is  quite  probable 
also  that  a  portion  of  this  transudate  is  reabsorbed  by  the  blood  vessels. 

Properties  and  Composition  of  Lymph  and  Chyle.  Lymph  as 
found  in  the  lymphatic  vessels  of  animals,  is  a  clear,  colorless  or  opalescent 
fluid,  having  an  alkaline  reaction,  a  saline  taste,  and  a  specific  gravity  of 
about  1.040.  It  holds  in  suspension  a  number  of  corpuscles,  resembling  in 
their  general  appearance  the  white  corpuscles  of  the  blood.  Their  number 
has  been  estimated  at  8200  per  cubic  millimetre,  though  the  number  varies 
in  different  portions  of  the  lymphatic  system.  As  the  lymph  flows  through 
the  lymphatic  gland,  it  receives  a  large  addition  of  corpuscles.  Lymph 
corpuscles  are  granular  in  structure,  and  measure  ^Wth  °f  an  inc^  i° 
diameter.  When  withdrawn  from  the  vessels,  lymph  undergoes  a  spon- 
taneous coagulation,  similar  to  that  of  the  blood,  after  which  it  separates  in 
serum  and  clot. 

COMPOSITION  OF  LYMPH. 

Water, 96.536 

Proteids  (serum-albumin,  fibrin-globulin), I-32° 

Extractives  (urea,  sugar,  cholesterine), I-559 

Fatty  matters, a  trace. 

Salts, 0.585 


100.000 


Chyle.  Chyle  is  the  fluid  found  in  the  lymphatic  vessels,  coming  from 
the  small  intestine  after  the  digestion  of  a  meal  containing  fat.  In  the 
intervals  of  digestion,  the  fluid  of  these  lymphatics  is  identical  in  all  respects 
with  the  lymph  found  in  all  other  regions  of  the  body.  As  soon  as 
the  emulsified  fat  passes  into  the  lymphatic  vessels,  and  mingles  with  the 
lymph,  it  becomes  milky  in  color,  and  the  vessels  which  previously  were 
invisible,  become  visible,  and  resemble  white  threads  running  between  the 


44  HUMAN   PHYSIOLOGY. 

layers  of  the  mesentery.  Chyle  has  a  composition  similar  to  that  of  lymph, 
but  it  contains  in  addition,  numerous  fatty  granules,  each  surrounded  by  an 
albuminous  envelope.  When  examined  microscopically,  the  chyle  presents 
a  fine  molecular  basis,  made  up  of  the  finely  divided  granules  of  fat. 

COMPOSITION  OF  CHYLE. 

Water, 902.37 

Albumin, 35. 1 6 

Fibrin, 3.70 

Extractives, 15.65 

Fatty  matters,    . 36.01 

Salts 7.11 

1000.00 

Forces  aiding  the  movement  of  Lymph  and  Chyle.  The  lymph  and 
chyle  are  continually  moving  in  a  progressive  manner,  from  the  periphery  or 
beginning  of  the  lymphatic  system,  to  the  final  termination  of  the  thoracic 
duct.  The  force  which  primarily  determines  the  movement  of  the  lymph, 
has  its  origin  in  the  beginnings  of  the  lymphatic  vessels,  and  depends  upon 
the  difference  in  pressure  here  and  the  pressure  in  the  thoracic  duct.  The 
greater  the  quantity  of  fluid  poured  into  the  lymph  spaces,  the  greater  will 
be  the  pressure  and  consequently  the  movement.  The  first  movement  of 
chyle  is  the  result  of  a  contraction  of  the  muscular  fibres  within  the  walls 
of  the  villus.  At  the  time  of  contraction,  the  lymphatic  capillary  is  com- 
pressed and  shortened,  and  its  contents  forced  onward  into  the  true  lym- 
phatic. When  the  muscular  fibres  relax,  regurgitation  is  prevented  by  the 
closure  of  the  valve  in  the  lymphatic  at  the  base  of  the  villus. 

As  the  walls  of  the  lymphatic  vessels  contain  muscular  fibres,  when  they 
become  distended,  these  fibres  contract  and  assist  materially  in  the  onward 
movement  of  the  fluid. 

The  contraction  of  the  general  muscular  masses  in  all  parts  of  the  body, 
by  exerting  an  intermittent  pressure  upon  the  lymphatics,  also  hastens  the 
current  onward ;  regurgitation  is  prevented  by  the  closure  of  valves  which 
everywhere  line  the  interior  of  the  vessels. 

The  respiratory  movements  aid  the  general  flow  of  both  lymph  and  chyle 
from  the  thoracic  duct  into  the  venous  blood.  During  the  time  of  an  inspi- 
ratory  movement,  the  pressure  within  the  thorax,  but  outside  the  lungs, 
undergoes  a  diminution  in  proportion  to  the  extent  of  the  movement;  as  a 
result,  the  fluid  in  the  thoracic  duct  outside  of  the  thorax,  being  under  a 
higher  pressure,  flows  more  rapidly  into  the  venous  system.  At  the  time 
of  an  expiration,  the  pressure  rises  and  the  flow  is  temporarily  impeded, 
only  to  begin  again  at  the  next  inspiration. 


45 


BLOOD. 

The  Blood  is  a  nutritive  fluid  containing  all  the  elements  necessary  for 
the  repair  of  the  tissues ;  it  also  contains  principles  of  waste  absorbed  from 
the  tissues,  which  are  conveyed  to  the  various  excretory  organs  and  by  them 
eliminated  from  the  body. 

The  total  amount  of  blood  in  the  body  is  estimated  to  be  about  one- eighth 
of  the  body  weight ;  from  1 6  to  18  pounds  in  an  individual  of  average  physi- 
cal development.  The  quantity  varies  during  the  24  hours;  the  maximum 
being  reached  in  the  afternoon,  the  minimum  in  the  early  morning  hours. 

Blood  is  a  heterogeneous,  opaque  red  fluid,  having  an  alkaline  reaction, 
a  saline  taste,  and  a  specific  gravity  of  1.055. 

The  opacity  is  due  to  the  refrac.tion  of  the  rays  of  light  by  the  elements 
of  which  the  blood  is  composed.  The  color  varies  in  hue,  from  a  bright 
scarlet  in  the  arteries  to  a  deep  purple  in  the  veins,  due  to  the  presence  of 
a  coloring  matter,  hemoglobin,  in  different  degrees  of  oxidation. 

The  alkalinity  is  constant,  and  depends  upon  the  presence  of  the  alka- 
line sodium  phosphate,  Na2  HPO4. 

The  saline  taste  is  due  to  the  amount  of  sodium  chloride  present. 

The  specific  gravity  ranges  within  the  limits  of  health,  from  1.045  to  1.075. 

The  odor  of  the  blood  is  characteristic,  and  varies  with  the  animal  from 
which  it  is  drawn,  due  to  the  presence  of  caproic  acid. 

The  temperature  of  the  blood  ranges  from  98°  Fahr.  at  the  surface  to 
107°  Fahr.  in  the  hepatic  vein;  it  loses  heat  by  radiation  and  evaporation 
as  it  approaches  the  extremities,  and  as  it  passes  through  the  lungs. 

Blood  consists  of  two  portions  : 

1.  The  Liquor  Sanguinis  or  Plasma,  a  transparent,  colorless  fluid,  in 
which  are  floating — 

2.  Red  and  white  corpusjes;  these  constituting  by  weight  less  than  one- 
half,  40  per  cent.,  of  the  entire  amount  of  blood.  • 

COMPOSITION  OF  PLASMA. 

DALTON. 

Water, 902.00 

Albumin, 53.00 

Paraglobulin, 22.00 

Fibrinogen,      3.00 

Fatty  matters, 2.50 

Crystallizable  nitrogenous  matters, 4.00 

Other  organic  matter, 5<o° 

Mineral  salts, 8.50 

1000.00 


46  HUMAN   PHYSIOLOGY. 

Water  acts  as  a  solvent  for  the  inorganic  matters  and  holds  in  suspension 
the  corpuscular  elements. 

Albumin  is  the  nutritious  principle  of  the  blood ;  it  is  absorbed  by  the 
tissues  to  repair  their  waste  and  is  transformed  into  the  organic  basis 
characteristic  of  each  structure. 

Paraglobulin  Q?  fibrinoplastin  is  a  soft  amorphous  substance  precipitated 
by  sodium  chloride  in  excess,  or  by  passing  a  stream  of  carbonic  acid 
through  dilute  serum. 

Fibrinogen  can  also  be  obtained  by  strongly  diluting  the  serum  and 
passing  carbonic  acid  through  it  for  a  long  time,  when  it  is  precipitated  as 
a  viscous  deposit. 

Fatty  matter  exists  in  small  proportion,  except  in  pathological  conditions 
and  after  the  ingestion  of  food  rich  in  oleaginous  matters ;  it  soon  disap- 
pears, undergoing  oxidation,  generating  heat  and  force,  or  is  deposited  as 
adipose  tissue. 

Sztgar  is  represented  by  glucose,  a  product  of  the  digestion  of  saccharine 
matter  and  starches  in  the  alimentary  canal ;  glycogenic  matter  is  derived 
from  the  liver. 

The  Saline  constititents  aid  the  process  of  osmosis,  give  alkalinity  to 
the  blood,  promote  the  absorption  of  carbonic  acid  from  the  tissues  into 
the  blood,  and  hold  other  substances  in  solution;  the  most  important 
are  the  sodium  and  potassium  chlorides,  the  calcium  and  magnesium 
phosphates. 

Excrementitious  matters  are  represented  by  carbonic  acid,  urea,  creatin, 
creatinin,  urates,  oxalates,  etc. ;  they  are  absorbed  from  the  tissues  by  the 
blood  and  conveyed  to  the  excretory  organs,  lungs,  kidneys,  etc. 

Gases.    Oxygen,  nitrogen  and  carbonic  acid  exist  in  varying  proportions. 


BLOOD  CORPUSCLES. 

The  corpuscular  elements  of  the  blood  occur  under  two  distinct  forms, 
which,  from  their  color,  are  known  as  the  red  and  white  corpuscles. 

The  Red  Corpuscles,  as  they  float  in  a  thin  layer  of  the  Liquor 
Sanguinis,  are  of  a  pale  straw  color ;  it  is  only  when  aggregated  in 
masses  that  they  assume  the  bright  red  color.  In  form  they  are  circu- 
lar and  biconcave;  they  have  an  average  diameter  of  the  ^^W  °^ 
an  inch. 

In  mammals,  birds,  reptiles,  amphibia  and  fish  the  corpuscles  vary  in 
size  and  number,  gradually  becoming  larger  and  less  numerous  as  the  scale 
of  animal  life  is  descended,  e.g.  : — 


47 


TABLE  SHOWING  COMPARATIVE  DIAMETER  OF  RED 
CORPUSCLES. 


^     Mammals. 

Birds. 

Reptiles. 

Amphibia. 

Fish. 

Man,                 S^OJT- 

Eagle, 

TH'IS- 

Turtle,      r^'sx- 

Frog, 

TlW 

Perch, 

2055- 

Chimpanzee,  53*15. 
Ourang,          33»g3. 

Owl, 

Sparrow, 

irW- 

Tortoise,  T515iJ. 
Lizard,      T^'BS- 

Toad, 
Proteus, 

Carp. 
Pike, 

2oW- 

D°S,                      3T&2- 

Swallow, 

TJT33- 

Viper,       1275- 

Siren, 

55ij. 

Eel,       , 

Cat,                  jsW- 

Pigeon, 

iS,. 

Amphiuma, 

3^- 

H°g,                       5335- 

Turkey, 

2055- 

Horse,             „*„„. 

Goose, 

rBW- 

Ox,                  52'S7. 

Swan, 

In  man  and  the  mammals  the  red  corpuscles  present  neither  a  nucleus 
nor  a  cell  wall,  and  are  universally  of  a  small  size.  They  can  be  readily 
distinguished  from  the  corpuscles  of  birds,  reptiles  and  fish,  in  which  they 
are  larger,  oval  in  shape  and  possess  a  well-defined  nucleus. 

The  red  corpuscles  are  exceedingly  numerous,  amounting  to  about 
5,000,000  in  a  cubic  millimetre  of  blood.  In  structure  they  consist  of  a 
firm,  elastic,  colorless  framework,  the  stroma,  in  the  meshes  of  which  is 
entangled  the  coloring  matter,  the  hemoglobin. 

CHEMICAL  COMPOSITION  OF  RED  CORPUSCLES. 

Water, 688.00 

Globulin, 282.22 

Haemoglobin, 16.75 

Fatty  matter, 2.31 

Extractives, 2.60 

Mineral  salts, 8.12 


Haemoglobin^  the  coloring  matter  of  the  corpuscles,  is  an  albuminous 
compound,  composed  of  C.  O.  H.  N.  S.  and  iron.  It  may  exist  either  in 
an  amorphous  or  crystalline  form.  When  deprived  of  all  its  oxygen, 
except  the  quantity  entering  into  its  intimate  composition,  the  haemoglobin 
becomes  dark  in  color,  somewhat  purple  in  hue,  and  is  known  as  reduced 
hemoglobin.  When  exposed  to  the  action  of  oxygen,  it  again  absorbs  a 
definite  amount  and  becomes  scarlet  in  color,  and  is  known  as  oxy-hemo- 
globin.  The  amount  of  oxygen  absorbed  is  1.76  c.cm.  (r7^  cubic  inch)  for 
I  milligramme  (^:?  grain)  of  haemoglobin. 

It  is  this  substance  which  gives  the  color  to  the  venous  and  arterial 
blood.  As  the  venous  blood  passes  through  the  capillaries  of  the  lungs, 
the  reduced  hemoglobin  absorbs  the  oxygen  from  the  pulmonary  air  and 
becomes  oxy-hcemoglobin,  scarlet  in  color,  and  the  blood  becomes  arterial. 
When  the  arterial  blood  passes  into  the  systemic  capillaries,  the  oxygen 


48  HUMAN    PHYSIOLOGY. 

is  absorbed  by  the  tissues,  the  haemoglobin  becomes  reduced,  purple  in 
color,  and  the  blood  becomes  venous.  A  dilute  solution  of  oxy-haemo- 
globin  gives  two  absorption  bands  between  the  lines  D  and  E  of  the 
solar  spectrum.  Reduced  haemoglobin  gives  but  one  absorption  band, 
occupying  the  space  existing  between  the  two  bands  of  the  oxy-hsemo- 
globin  spectrum. 

The  Function  of  the  red  corpuscle  is,  therefore,  to  absorb  oxygen  and 
carry  it  to  the  tissues;  the  smaller  the  corpuscles  and  the  greater  the 
number,  the  greater  is  the  quantity  of  oxygen  absorbed  ;  and,  consequently, 
all  the  vital  functions  of  the  body  become  more  active. 

The  White  Corpuscles  are  far  less  numerous  than  the  red,  the  proportion 
being,  on  an  average,  about  I  white  to  350  or  400  red.;  they  are  globular 
in  shape,  and  measure  the  ^sVtf  °f  an  inch  m  diameter,  and  consist  of  a 
soft,  granular,  colorless  substance,  containing  several  nuclei. 

The  white  corpuscles  possess  the  power  of  spontaneous  movement,  alter- 
nately contracting  and  expanding,  throwing  out  processes  of  their  substance 
and  quickly  withdrawing  them,  thus  changing  their  shape  from  moment 
to  moment.  These  movements  resemble  those  of  the  amoeba,  and  for  this 
reason  are  termed  amoeboid.  They  also  possess"  the  capability  of  moving 
from  place  to  place.  In  the  interior  of  the  vessels  they  adhere  to  the  inner 
surface,  while  the  red  corpuscles  move  through  the  centre  of  the  stream. 

The  white  corpuscles  are  identical  with  the  leucocytes,  and  are  found 
in  milk,  lymph,  chyle  and  other  fluids. 

Origin  of  Corpuscles.  The  red  corpuscles  take  their  origin  from  the 
mesoblastic  cells  in  the  vascular  area  of  the  developing  embryo. 

In  the  adult  they  are  produced  from  colorless  nucleated  corpuscles 
resembling  the  white  corpuscles.  The  spleen  is  the  organ  in  which  they 
are  finally  destroyed. 

The  white  corpuscles  originate  from  the  leucocytes  of  the  adenoid  tissue, 
and  subsequently  give  rise  to  the  red  corpuscles  and  partly  to  new  tissues 
that  result  from  inflammatory  action. 


COAGULATION  OF  THE  BLOOD. 

When  blood  is  withdrawn  from  the  body  and  allowed  to  remain  at  rest, 
it  becomes  somewhat  thick  and  viscid  in  from  three  to  five  minutes ;  this 
viscidity  gradually  increases  until  the  entire  volume  of  blood  assumes  a 
jelly-like  consistence,  which  occupies  from  five  to  fifteen  minutes. 

As  soon  as  coagulation  is  completed,  a  second  process  begins,  which 
consists  in  the  contraction  of  the  coagulum  and  the  oozing  of  a  clear,  straw- 


BLOOD.  49 

colored  liquid,  the  scrum,  which  gradually  increases  in  quantity  as  the  clot 
diminishes  in  size,  by  contraction,  until  the  separation  is  completed,  which 
occupies  from  12  to  24  hours. 

The  changes  in  the  blood  are  as  follows : — 

Before  coagulation. 

f    Liq.  Sanguinis           "j  f  Water. 

or                      V    Consisting,  of  J  Albumin. 

Living  blood,    -j     Plasma.                       J  |  Fibrinogen. 

L  Salts. 

[    Corpuscles.     Red  and  white. 
After  coagulation. 

f    Crassamentum.          1    n     .  .  .  f  Fibrin. 

I    Clot  or  coagulum.     /    Containing  \  Corpuscles. 

Dead  blood,      -j  f  Water. 

|     Serum.                             Containing  -]  Albumin. 

L  I  Salts. 

The  serum,  therefore,  differs  from  the  Liquor  Sanguinis  in  not  containing 
fibrin. 

In  from  12  to  24  hours  the  upper  surface  of  the  clot  presents  a  grayish 
appearance,  the  buffy  coat,  which  is  due  to  the  rapid  sinking  of  the  red 
corpuscles  beneath  the  surface,  permitting  the  fibrin  to  coagulate  without 
them,  which  then  assumes  a  grayish  yellow  tint.  Inasmuch  as  the  white 
corpuscles  possess  a  lighter  specific  gravity  than  the  red,  they  do  not  sink 
so  rapidly,  and  becoming  entangled  in  the  fibrin,  assist  in  forming  the  buffy 
coat.  Continued  contraction  gives  a  cupped  appearance  to  the  surface  of 
the  clot. 

Inflammatory  states  of  the  blood  produce  a  marked  increase  in  the 
buffed  and  cupped  condition,  on  account  of  the  aggregation  of  the  cor- 
puscles, and  their  tendency  to  rapid  sinking. 

Nature  of  Coagulation.  Coagulated  fibrin  does  not  preexist  in  the 
blood,  but  is  formed  at  the  moment  blood  is  withdrawn  from  the  vessels. 
According  to  Denis,  a  liquid  substance,  plasmine,  exists  in  the  blood, 
which,  when  withdrawn  from  the  circulation,  decomposes  m^o  fibrin  and 
met-albumin. 

According  to  Schmidt,  fibrin  results  from  the  union  of  fibrinoplastin 
(paraglobulin)  and  fibrinogen,  brought  about  by  the  presence  of  a  third 
substance,  the  fibrin  ferment. 

According  to  Hammersten  and  others,  the  fibrin  obtained  from  the  blood 
after  coagulation,  comes  from  the  fibrinogen  alone,  the  conversion  being 
brought  about  by  the  presence  of  a  ferment  substance,  paraglobulin  in  this 


50  HUMAN    PHYSIOLOGY. 

case  having  nothing  to  do  with  the  change.  This  view  is  supported  by  the 
fact  that  the  quantity  of  fibrin  obtained  from  the  blood  is  never  greater  than 
the  quantity  of  fibrinogen  previously  present.  The  origin  of  the  ferment  is 
obscure,  but  there  is  reason  to  believe  that  it  comes  from  the  injured  vascu- 
lar coats  or  from  the  breaking  of  the  white  corpuscles. 

Conditions  Influencing  Coagulation.  The  process  is  retarded  by 
cold,  retention  within  living  vessels,  neutral  salts  in  excess,  inflammatory 
conditions  of  the  system,  imperfect  aeration,  exclusion  from  air,  etc. 

It  is  hastened  by  a  temperature  of  100°  F.,  contact  with  air,  rough  sur- 
faces and  rest. 

Blood  coagulates  in  the  body  after  the  arrest  of  the  circulation  in  the 
course  of  12  to  24  hours;  local  arrest  of  the  circulation,  from  compression 
or  a  ligature,  will  cause  coagulation,  thus  preventing  hemorrhages  from 
wounded  vessels. 

The  Composition  of  the  Blood  varies  in  different  portions  of  the  body. 
The  arterial  differs  from  the  venous,  in  being  more  coagulable,  in  contain- 
ing more  oxygen  and  less  carbonic  acid,  in  having  a  bright  scarlet  color, 
from  the  union  of  oxygen  with  haemoglobin ;  the  purple  hue  of  venous  blood 
results  from  the  deoxidation  of  the  coloring  matter. 

The  blood  of  the  portal  vein  differs  in  constitution,  according  to  different 
stages  of  the  digestive  process;  during  digestion  it  is  richer  in  water, 
albuminous  matter  and  sugar ;  occasionally  it  contains  fat ;  corpuscles  are 
diminished,  and  there  is  an  absence  of  biliary  substances. 

The  blood  of  the  hepatic  vein  contains  a  larger  proportion  of  red  and 
white  corpuscles;  the  sugar  is  augmented,  while  albumin,  fat  and  fibrin 
are  diminished. 

Pathological  conditions  of  the  blood. 

I.  Plethora — increase  in  the  volume  or  quantity  of  blood. 

3,  Anamia — deficiency  of  red  globules  with  increase  of  water. 

3.  Leucocylhemia — increase  of  white  and  diminution  of  red  corpuscles. 

4.  Glycohcemia — excess  of  sugar  in  the  blood. 

5.  Urccmia — increase  in  the  amount  of  urea. 

6.  Cholestercemia — an  excess  of  cholesterine  in  the  blood. 

7.  Throjnbosis   and   embolism — clotting   of    blood    in    the   vessels   and 
dissemination  of  coagula. 

8.  Lipcemia — an  excess  of  fat. 

9.  Melancemia — pigment  in  the  blood. 


CIRCULATION  OF  THE  BLOOD.  51 

CIRCULATION  OF  THE  BLOOD. 

The  Circulatory  Apparatus  by  which  the  blood  is  distributed  to  all 
portions  of  the  body  consists  of  a  central  organ,  the  heart,  with  which  is 
connected  a  system  of  closed  vessels,  known  as  arteries,  capillaries  and  veins. 
Within  this  system  the  blood  is  kept,  by  the  action  of  the  heart,  in  continual 
movement,  distributing  nutritious  matter  to  all  portions  of  the  body  and 
carrying  waste  matters  from  the  tissues  to  the  various  eliminating  organs. 

The  heart  is  a  hollow  muscular  organ,  pyramidal  in  shape,  measuring 
about  5^  inches  in  length,  about  3^  in  breadth,  weighing  from  10-12  oz. 
in  the  male  and  from  8-10  oz.  in  the  female.  Situated  in  the  thoracic 
cavity,  between  the  lungs,  its  base  is  directed  upward,  backward  and  to  the 
right,  its  apex  is  directed  downward  and  to  the  left. 

Pericardium.  The  heart  is  surrounded  by  a  closed  fibrous  membrane 
called  the  pericardium.  The  inner  surface  of  this  membrane  is  lined  by  a 
serous  membrane,  which  is  also  reflected  over  the  surface  of  the  heart ; 
between  the  two  surfaces  of  the  serous  membrane  is  found  a  small  quantity 
of  fluid,  the  pericardial  fluid,  which  lubricates  the  surfaces  and  prevents 
friction  during  the  movements  of  the  heart.  The  interior  of  the  heart  is  also 
lined  by  a  serous  membrane  called  the  endo-cardium. 

Cavities  of  the  Heart.  The  general  cavity  of  the  heart  is  subdivided 
by  a  longitudinal  septum  into  a  right  and  left  half;  each  of  these  cavities  is 
in  turn  subdivided  by  a  transverse  constriction  into  two  smaller  cavities 
which  communicate  with  each  other  and  are  known  as  the  auricles  and 
ventricles.  The  orifice  between  the  auricle  and  ventricle  being  known  as 
the  auriculo-ventricular  orifice.  The  heart  therefore  consists  of  four 
cavities,  a  right  auricle  and  ventricle  and  a  left  auricle  and  ventricle. 

Into  the  right  auricle,  the  two  terminal  trunks  of  the  venous  system,  the 
superior  and  inferior  vence  ca'vte,  empty  the  venous  blood  which  has  been 
collected  from  all  parts  of  the  system ;  from  the  right  ventricle  arises  the 
pTilmonary  artery  which  passing  into  the  lungs,  distributes  the  blood  to  the 
walls  of  the  air  cells  of  the  lungs ;  into  the  left  auricle  empty  {our  pulmonary 
veins  which  have  collected  the  blood  from  the  lung  capillaries;  from  the 
left  ventricle  springs  the  aorta,  the  general  trunk  of  the  arterial  system 
whose  branches  distribute  the  blood  to  the  entire  system. 

The  Valves  of  the  Heart.  The  valves  of  the  heart  are  formed  by  a 
reduplication  of  the  endocardium  strengthened  by  connective  tissue.  At  the 
auriculo-ventricular  openings  on  the  right  and  left  sides  of  the  heart  respec- 
tively are  found  the  triciispid  and  mitral  valves.  The  tricuspid  valve 


52  HUMAN    PHYSIOLOGY. 

consists  of  three,  the  mitral  of  two  cusps  or  segments  which  project  into 
the  interior  of  the  ventricle  when  it  does  not  contain  blood.  At  their  bases 
the  segments  are  united  so  as  to  form  an  annular  membrane  attached*  to  the 
margin  of  the  orifice.  To  the  free  edges  of  the  valves  are  attached  numerous 
fine  threads,  the  chorda  tendinece  which  are  the  tendons  of  the  small  papillary 
muscles  springing  from  the  walls  of  the  ventricles. 

The  Semilunar  Valves.  At  the  openings  of  the  pulmonary  artery  and 
the  aorta  are  found  three  cupped-shaped  or  semilunar  valves,  the  free  edges 
of  which  are  directed  away  from  the  interior  of  the  heart.  The  anatomical 
arrangement  of  the  valves  is  such  that  upon  their  closure  regurgitation  of 
the  blood  is  prevented. 

Movement  of  the  Blood.  The  blood  within  the  vascular  apparatus  is 
in  continual  movement  from  the  left  side  of  the  heart  through  the  arterial  sys- 
tem, capillaries  and  veins  to  the  right  side,  and  from  the  right  side  through 
the  pulmonary  artery,  capillaries  and  veins  to  the  original  point  of  departure. 
The  cause  of  this  movement  is  the  difference  of  pressure  which  exists 
between  the  blood  within  the  aorta  and  the  terminations  of  the  venae  cavae, 
and  between  the  blood  of  the  pulmonary  artery  and  the  pulmonary  veins. 

The  function  of  the  heart  is  to  propel  the  blood  through  the  blood-ves- 
sels, which  it  does  by  raising  or  maintaining  this  higher  pressure  in  the 
aorta  and  pulmonary  artery.  This  is  accomplished  by  alternate  contrac- 
tions and  relaxations  of  its  muscular  walls.  These  two  movements  are 
known  respectively  as  the  systole  and  the  diastole. 

Course  of  the  Blood  through  the  Heart.  The  venous  blood  re- 
turned to  the  heart  by  the  superior  and  inferior  venae  cavse  is  emptied  during 
the  diastole  into  the  right  auricle,  in  the  contraction  of  which  it  is  forced 
through  the  right  auriculo-ventricular  opening  into  the  right  ventricle  and 
distends  it.  Upon  the  contraction  of  the  ventricle  the  blood  is  propelled 
through  the  pulmonary  artery  into  the  lungs,  where  it  undergoes  aeration 
and  is  changed  in  color. 

The  arterial  blood  is  now  collected  by  the  pulmonary  veins  and  poured 
into  the  left  auricle ;  thence  it  passes  into  the  left  ventricle,  which  becomes 
fully  distended.  Upon  the  contraction  of  the  ventricle,  the  blood  is  pro- 
pelled into  the  aorta,  and  by  it  distributed  to  the  system  at  large,  to  be  again 
returned  to  the  heart  by  the  veins. 

Regurgitation  from  the  ventricles  into  the  auricles  during  the  systole  is 
prevented  by  the  closure  of  the  tricuspid  and  mitral  valves;  regurgitation 
from  the  pulmonary  artery  and  aorta  into  the  ventricles  during  the  diastole 
is  prevented  by  the  closure  of  the  semilunar  valves. 


CIRCULATION   OF  THE  BLOOD. 


53 


While  there  is  but  one  circulation  physiologists  frequently  divide  the  cir- 
culatory apparatus  into : — 

1.  The  Systemic  Circulation,  which  includes  the  movement  of  the  blood 
from  the  left  side  of  the  heart  through  the 

aorta  and  its  branches,  through  the  capilla- 
ries and  veins  to  the  right  side. 

2.  The   Pulmonary  Circulation,  which 
includes  the  course  of  the  blood  from  the 
right  side  through  the   pulmonary  artery, 
through  the    capillaries  of  the  lungs   and 
pulmonary   veins   to   me   left   side  of  the 
heart. 

3.  The   Portal   Circulation,   which    in- 
cludes the  portal  vein.     This  is  formed  by 
the  union  of  the  radicles  of  the  gastric, 
mesenteric  and  splenic  veins,  and  carries 
the  blood  directly  into  the  liver,  where  the 
vein   again    divides   into   a   fine   capillary 
plexus  from  which  the  hepatic  veins  arise 
which  empty  into  the  ascending  venae  cavae. 

Movements  of  the  Heart.  At  each 
revolution,  during  the  systole,  the  heart 
hardens  and  becomes  shortened  in  its  long 
diameter ;  its  apex  is  raised  up,  rotated  on 
its  axis  from  left  to  right  and  thrown  for- 
ward against  the  walls  of  the  chest.  The 
impulse  of  the  heart,  observed  about  two 
inches  below  the  nipple,  and  one  inch  to 
the  sternal  side,  between  the  fifth  and  sixth 
ribs,  is  caused  mainly  by  the  apex  of  the 

heart  striking  against  the  chest  walls,  as-  a,  right,  I,  left  auricle ;  A,  right,  B, 

left  ventricle  ;  i ,  pulmonary  artery  ; 
2,  aorta;    /,  area  of   pulmonary, 


SCHEME  OF  THE  CIRCULATION. 


sisted  by  the  distention  of  the  great  vessels 
about  the  base  of  the  heart. 


K,  area  of  systemic  circulation; 
o,  the  superior  vena  cava  ;  G,  area 
supplying  the  inferior  vena  cava,  u; 
d,  d,  intestine ;  m,  mesenteric  ar- 
tery ;  q,  portal  vein ;  L,  liver ;  h, 
hepatic  vein. — From  Landois. 


Sounds  of  the  Heart.  If  the  ear  be 
placed  over  the  cardiac  region,  two  distinct 
sounds  are  heard  during  each  revolution  of 
the  heart,  closely  following  each  other  and  which  differ  in  character. 

The  sound  coinciding  with  the  systole  in  point  of  time,  the  first  sound, 
is  long  and  dull,  and  caused  by  the  closure  and  vibration  of  the  auriculo- 


54  HUMAN   PHYSIOLOGY. 

ventricular  valves,  the  contraction  of  the  walls  of  the  ventricles  and  the 
apex  beat ;  the  second  sound,  occurring  during  the  diastole,  is  short  and 
sharp,  and  caused  by  the  closure  o'f  the  semilunar  valves. 

.  The  capacity  of  the  left  ventricle  when  fully  distended  is  estimated  at 
from  four  to  seven  ounces. 

The  frequency  of  the  heart's  action  varies  at  different  periods  of  life, 
but  in  the  adult  male  it  beats  about  72  times  per  minute.  It  is  influenced 

by  age,  exercise,  posture,  digestion,  etc. 

• 
Age.    Before  birth,  the  number  of  pulsations  per  minute  averages  140 

During  the  first  year  it  diminishes  to,    .    * 128 

During  the  third  year  diminishes  to,      95 

From  the  eighth  to  the  fourteenth  year  averages,     ....    84 
In  adult  life  the  average  is, 72 

Exercise  and  digestion  increase  the  frequency  of  the  heart's  action. 

Posture  influences  the  number  of  pulsations  per  minute ;  in  the  male, 
standing,  the  average  is  8l ;  sitting,  71;  lying,  66 ;  independent,  for  the 
most  part,  of  muscular  effort. 

The  Rhythmical  movements  of  the  heart  are  dependent  upon — i. 
An  inherent  irritability  of  the  muscular  fibre,  which  manifests  itself  as  long 
as  the  nutrition  is  maintained.  2.  The  continuous  flow  of  blood  through 
its  cavities,  distending  them  and  stimulating  the  endocardium. 

The  force  exerted  by  the  left  ventricle  at  each  contraction  has  been 
estimated  at  52  pounds.  If  a  tube  be  inserted  into  the  aorta,  the  pressure 
there  will  be  sufficient  to  support  a  column  of  blood  nine  feet  or  a  column 
of  mercury  six  inches  in  height,  the  weight  in  either  case  being  about  four 
pounds.  The  estimation  of  the  force  which  the  heart  is  required  to  exert 
to  support  this  column  of  blood,  is  arrived  at  by  multiplying  the  pressure 
in  the  aorta  (4  pounds)  by  the  area  of  the  internal  surface  of  the  left 
ventricle  (about  13  inches).  Each  inch  of  the  ventricle  being  capable  of 
supporting  a  downward  pressure  of  4  pounds. 

Work  done  by  the  Heart.  The  work  done  by  the  heart  is  estimated 
by  multiplying  the  amount  of  blood  sent  out  from  the  right  and  left  ventricles 
at  each  contraction,  by  the  pressure  in  the  pulmonary  artery  and  aorta 
respectively,  e.  g:,  when  the  right  ventricle  contracts,  it  forces  out  one- 
quarter  pound  of  blood,  and  in  so  doing  must  overcome  a  pressure  in  the 
pulmonary  artery  sufficient  to  support  a  column  of  blood  three  feet  in 
height ;  that  is,  must  exert  energy  sufficient  to  raise  }£  Ib.  3  feet,  or  j^  X  3 
or  %  It),  one  foot.  When  the  left  ventricle  contracts,  it  sends  out  ^  Ib.  of 
blood,  and  in  so  doing,  the  left  ventricle  must  overcome  a  pressure  in  the 


CIRCULATION   OF  THE  BLOOD.  55 

aorta  sufficient  to  support  a  column  of  blood  nine  feet  in  height ;  that  is, 
must  exert  energy  sufficient  to  raise  tf  Ib.  9  feet,  or  #  X  9  or  2X  ll)S-  one 
foot.  Work  done  is  estimated  by  the  amount  of  energy  required  to  raise 
a  definite  weight  a  definite  height,  the  unit,  the  foot  pound,  being  that 
required  to  raise  one  pound  one  foot. 

The  heart,  therefore,  at  each  systole  exerts  energy  sufficient  to  raise  3  foot 
pounds,  and  as  it  contracts  72  times  per  minute,  it  would  raise  in  that 
time  3  X  72  or  2l6  foot  pounds;  and  in  one  hour  216  X  6o or  12,960 foot 
pounds;  and  in  24  hours  12,960  X  24  or  3II>°4°  foot  pounds  or  138.5 
foot  tons 

Influence  of  the  Nervous  System  upon  the  Heart.  When  the 
heart  of  a  frog  is  removed  from  the  body,  it  continues  to  beat  for  a 
variable  length  of  time,  depending  upon  the  nature  of  the  conditions 
surrounding  it.  The  heart  of  warm-blooded  animals  continues  to  beat 
but  for  a  very  short  time.  The  cause  of  the  continued  pulsations  of  the 
frog  heart  is  the  presence  of  nervous  ganglia  in  its  substance.  These 
ganglia  have  not  been  shown  to  exist  in  the  mammalian  heart,  but 
there  is  reason  to  believe  that  the  nervous  mechanism  is  fundamentally 
the  same. 

The  ganglia  of  the  heart  are  three  in  number,  one  situated  at  the  opening 
of  the  inferior  vena  cava  (the  ganglion  of  Remak),  a  second  situated 
in  the  auriculo-ventricular  septum  (the  ganglion  of  Bidder),  and  a  third 
situated  in  the  inter-auricular  septum  (the  ganglion  of  Ludwig).  The  first 
two  are  motor  in  function  and  excite  the  pulsations  of!  the  heart ;  the  third 
is  inhibitory  in  function  and  retards  the  action  of  the  heart.  The  actions 
of  these  ganglia,  though  for  the  most  part  automatic,  are  modified  by  im- 
pressions coming  through  nerves  from  the  medulla  oblongata.  When  the 
inhibitory  centre  is  stimulated  by  muscarin,  the  heart  is  arrested  in  diastole  ; 
when  atropia  is  applied,  the  heart  recommences  to  beat,  because  atropia 
paralyzes  the  inhibitory  centre. 

The  nerves  modifying  the  action  of  the  heart  are  the  Pneumogastric 
(Vagus)  and  the  Accelerator  nerves. 

The  Pneumogastric  nerve,  after  emerging  from  the  medulla,  receives 
motor  fibres  from  the  spinal  accessory  nerve.  It  then  passes  downward, 
giving  off  branches,  some  of  which  terminate  in  the  inhibitory  ganglion. 
Stimulation  of  the  vagus  by  increasing  the  activity  of  the  inhibitory  centre 
arrests  the  heart  in  diastole  with  its  cavities  full  of  blood ;  but  as  the  stimu- 
lation is  only  temporary,  after  a  few  seconds  the  heart  recommences  to 
beat;  at  first  the  pulsations  are  weak  and  feeble,  but  soon  regain  their 
original  vigor.  After  the  administration  of  atropia  in  sufficient  doses  to  de- 


56  HUMAN   PHYSIOLOGY. 

stroy  the  termination  of  the  pneumogastric,  stimulation  of  its  trunk  has  no 
effect  upon  the  heart.  The  inhibitory  fibres  in  the  vagus  are  constantly 
in  action,  for  division  of  the  nerve  on  both  sides  is  always  followed  by  an 
increase  in  the  frequency  of  the  heart's  pulsations. 

The  Accelerator  fibres  arise  in  the  medulla,  pass  down  the  cord,  emerge 
in  the  cervical  region,  pass  to  the  last  cervical  and  first  dorsal  ganglia  of  the 
sympathetic,  and  thence  to  the  heart.  Stimulation  of  these  fibres  causes  an 
increased  frequency  of  the  heart's  pulsations,  but  they  are  diminished  in 
force. 

ARTERIES. 

The  Arteries  are  a  series  of  branching  tubes  conveying  blood  to  all 
portions  of  the  body.  They  are  composed  of  three  coats — 

1.  External,  formed  of  areolar  and  elastic  tissue. 

2.  Middle,  contains  both   elastic  and  muscular  fibres,  arranged  trans- 

versely to  the  long  axis  of  the  artery.     The  elastic  tissue  is  more 
abundant  in  the  larger  vessels,  the  muscular  in  the  smaller. 

3.  Internal,  composed  of  a  thin  homogeneous  membrane,  covered  with 

a  layer  of  elongated  endothelial  cells. 

The  arteries  possess  both  elasticity  and  contractility. 

The  Property  of  Elasticity  allows  the  arteries  already  full  to  accommo- 
date themselves  to  the  incoming  amount  of  blood,  and  to  convert  the 
intermittent  acceleration  of  blood  in  the  large  vessels  into  a  steady  and 
continuous  stream  in  the  capillaries. 

The  Contractility  of  the  smaller  vessels  equalizes  the  current  of  blood, 
regulates  the  amount  going  to  each  part,  and  promotes  the  onward  flow  of 
blood. 

Blood  Pressure.  Under  the  influence  of  the  ventricular  systole,  the 
recoil  of  the  elastic  walls  of  the  arteries,  and  the  resistance  offered  by  the 
capillaries,  the  blood  is  constantly  being  subjected  to  a  certain  amount  of 
pressure.  If  a  large  artery  of  an  animal  be  divided,  and  a  glass  tube  of 
the  same  calibre  be  inserted  into  its  orifice,  the  blood  will  rise  to  a  height 
of  about  nine  feet ;  or  if  it  be  connected  with  a  mercurial  manometer,  the 
mercury  will  rise  to  a  height  of  six  inches.  This  height  will  be  a  measure 
of  the  pressure  in  the  vessel.  The  absolute  quantity  of  mercury  sustained 
by  an  artery  can  be  arrived  at  by  multiplying  the  height  of  the  column  by 
the  area  of  a  transverse  section  of  that  artery. 

The  pressure  of  the  blood  is  greatest  in  the  large  arteries,  but  gradually 
decreases  toward  the  capillaries. 


ARTERIES.  57 

The  blood  pressure  is  increased  or  diminished  by  influences  acting  upon 
the  heart  or  upon  the  peripheral  resistance  of  the  capillaries,  viz. : — 

If,  while  the  force  of  the  heart  remains  the  same,  the  number  of  pulsa- 
tions per  minute  increases,  thus  increasing  the  volume  of  blood  in  the 
arteries,  the  pressure  rises.  If  the  rate  remains  the  same,  but  the  force 
increases,  the  pressure  again  rises.  Causes  that  increase  the  peripheral 
resistance  by  contracting  the  arterioles,  e.  g.,  vasomotor  nerves,  cold,  etc., 
produce  an  increase  of  the  pressure. 

On  the  other  hand,  influences  which  diminish  either  the  volume  of  the 
blood,  or  the  number  of  pulsations,  or  the  force  of  the  heart,  or  the  peri- 
pheral resistance,  lower  the  pressure. 

The  Pulse  is  the  sudden  distention  of  the  artery  in  a  transverse  and 
longitudinal  direction,  due  to  the  injection  of  a  volume  of  blood  into  the 
arteries  at  the  time  of  the  ventricular  systole.  As  the  vessels  are  already 
full  of  blood,  they  must  expand  in  order  to  accommodate  themselves  to  the 
incoming  volume  of  blood.  The  blood  pressure  is  thus  increased,  and  the 
pressure  originating  at  the  ventricle  excites  a  pulse  wave,  which  passes 
from  the  heart  toward  the  capillaries  at  the  rate  of  about  twenty-nine  feet 
per  second.  It  is  this  wave  that  is  appreciated  by  the  finger. 

The  Velocity  with  which  the  blood  flows  in  the  arteries  diminishes  from 
the  heart  to  the  capillaries,  owing  to  an  increase  of  the  united  sectional  area 
of  the  vessels,  and  increases  in  rapidity  from  the  capillaries  toward  the 
heart.  It  moves  most  rapidly  in  the  large  vessels,  and  especially  under 
the  influence  of  the  ventricular  systole.  From  experiments  on  animals, 
it  has  been  estimated  to  move  in  the  carotid  of  man  at  the  rate  of  sixteen 
inches  per  second,  and  in  the  large  veins  at  the  rate  of  four  inches  per 
second. 

The  Calibre  of  the  blood  vessels  is  regulated  by  the  vasomotor 
nerves,  which  have  their  origin  in  the  gray  matter  of  the  medulla  oblongata. 
They  issue  from  the  spinal  cord  through  the  anterior  roots  of  spinal  nerves, 
pass  through  the  sympathetic  ganglia,  and  ultimately  are  distributed  to  the 
coats  of  the  blood  vessels.  They  exert,  at  different  times,  a  constricting  and 
dilating  action  upon  the  vessels,  thus  keeping  up  the  arterial  tonus. 

Capillaries.  The  capillaries  constitute  a  network  of  vessels  of  micro 
scopic  size,  which  distribute  the  blood  to  the  inmost  recesses  of  the  tissues, 
inosculating  with  the  arteries  on  the  one  hand  and  the  veins  on  the  other ; 
they  branch  and  communicate  in  every  possible  direction. 

The  diameter  of  a  capillary  vessel  varies  from  the  ^Vtf  to  ^e  3uW  °f 
an  inch;    their  walls  consist  of  a  delicate  homogeneous  membrane,  the 
E 


58  HUMAN   PHYSIOLOGY. 

2(jtf(HF  °f  an  *nch  *n  thickness,  lined  by  flattened,  elongated,  endothelial 
cells,  between  which,  here  and  there,  are  observed  stomata. 

It  is  through  the  agency  of  the  capillary  vessels  that  the  phenomena  of 
nutrition  and  secretion  takes  place,  for  here  the  blood  flows  in  an  equable 
and  continuous  current,  and  is  brought  into  intimate  relationship  with  the 
tissues,  two  of  the  essential  conditions  for  proper  nutrition. 

The  rate  of  movement  in  the  capillary  vessels  is  estimated  at  one  inch 
in  thirty  seconds. 

In  the  capillary  current  the  red  corpuscles  may  be  seen  hurrying  down 
the  centre  of  the  stream,  while  the  white  corpuscles  in  the  still  layer 
adhere  to  the  walls  of  the  vessel,  and  at  times  can  be  seen  to  pass  through 
the  walls  of  the  vessel  by  amoeboid  movements. 

The  passage  of  the  blood  through  the  capillaries  is  mainly  due  to  the 
force  of  the  ventricular  systole  and  the  elasticity  of  the  arteries ;  but  it  is 
probably  also  aided  by  a  power  resident  in  the  capillaries  themselves,  the 
result  of  a  vital  relation  between  the  blood  and  the  tissues. 

The  Veins  are  the  vessels  which  return  the  blood  to  the  heart ;  they 
have  their  origin  in  the  venous  radicles,  and  as  they  approach  the  heart, 
converge  to  form  larger  trunks,  and  terminate  finally  in  the  venae  cavae. 

They  possess  three  coats — 

I .  External^  made  up  of  areolar  tissue. 

2..  Middle,  composed  of  non-striated  muscular  fibres,  yellow,  elastic  and 
fibrous  tissue. 

3.  Internal,  an  endothelial  membrane,  similar  to  that  of  the  arteries. 

Veins  are  distinguished  by  the  possession  of  valves  throughout  their 
course,  which  are  arranged  in  pairs,  and  formed  by  a  reflection  of  the  inter- 
nal coat,  strengthened  by  fibrous  tissues;  they  always  look  toward  the  heart, 
and  when  closed  prevent  a  return  of  blood  in  the  veins.  Valves  are  most 
numerous  in  the  veins  of  the  extremities,  but  are  entirely  absent  in  many 
others. 

The  onward  flow  of  blood  in  the  veins  is  mainly  due  to  the  action  of 
the  heart;  but  is  assisted  by  the  contraction  of  the  voluntary  muscles  and 
the  force  of  respiration. 

Muscular  contraction,  which  is  intermittent,  aids  the  flow  of  blood  in 
the  veins,  by  compressing  them.  As  regurgitation  is  prevented  by  the 
closure  of  the  valves,  the  blood  is  forced  onward  toward  the  heart. 

Rhythmical  movements  of  veins  have  been  observed  in  some  of  the  lower 
animals,  aiding  the  onward  current  of  blood. 

During  the  movement  of  inspiration  the  thorax  is  enlarged  in  all  its 


RESPIRATION.  69 

diameters,  and  the  pressure  on  its  contents  at  once  diminishes.  Under 
these  circumstances  a  suction  force  is  exerted  upon  the  great  venous  trunks, 
which  causes  the  blood  to  flow  with  increased  rapidity  and  volume  toward 
the  heart. 

Venous  pressure.  As  the  force  of  the  heart  is  nearly  expended  in 
driving  the  blood  through  the  capillaries,  the  pressure  in  the  venous  system 
is  not  very  marked,  not  amounting  in  the  jugular  vein  of  a  dog  to  more 
than  Jj  that  of  the  carotid  artery. 

The  time  required  for  a  complete  circulation  of  the  blood  throughout  the 
vascular  system  has  been  estimated  to  be  from  20  to  30  seconds,  while  for 
the  entire  mass  of  blood  to  pass  through  the  heart  58  pulsations  would  be 
required,  occupying  48  seconds. 

The  Forces  keeping  the  blood  in  circulation  are — 

1.  Action  of  the  heart. 

2.  Elasticity  of  the  arteries. 

3.  Capillary  force. 

4.  Contraction  of  the  voluntary  muscles  upon  the  veins. 

5.  Respiratory  movements. 


RESPIRATION. 

Respiration  is  the  function  by  which  oxygen  is  absorbed  into  the 
blood  and  carbonic  acid  exhaled.  The  appropriation  of  the  oxygen  and 
the  evolution  of  carbonic  acid  takes  place  in  the  tissues  as  a  part  of  the 
general  nutritive  process ;  the  blood  and  respiratory  apparatus  constituting 
the  media  by  means  of  which  the  interchange  of  gases  is  accomplished. 

The  Respiratory  Apparatus  consists  of  the  larynx,  trachea  and  lungs. 

The  Larynx  is  composed  of  firm  cartilages,  united  together  by  liga- 
ments and  muscles;  running  antero-posteriorly  across  the  upper  opening  are 
four  ligamentous  bands,  the  two  superior,  or  false  vocal  cords,  and  the  two 
inferior,  or  true  vocal  cords,  formed  by  folds  of  the  mucous  membrane. 
They  are  attached  anteriorly  to  the  thyroid  cartilages  and  posteriorly  to  the 
arytenoid  cartilages  and  are  capable  of  being  separated  by  the  contraction 
of  the  posterior  crico-arytenoid  muscles,  so  as  to  admit  the  passage  of  air 
into  and  from  the  lungs. 

The  Trachea  is  a  tube  from  four  to  five  inches  in  length,  three-quarters 
of  an  inch  in  diameter,  extending  from  the  cricoid  cartilage  of  the  larynx 
to  the  third  dorsal  vertebra,  where  it  divides  into  the  right  and  left  bronchi. 


60 


HUMAN   PHYSIOLOGY. 


It  is  composed  of  a  series  of  cartilaginous  rings,  which  extend  about  two- 
thirds  around  its  circumference,  the  posterior  third  being  occupied  by  fibrous 
tissue  and  non-striated  muscular  fibres  which  are  capable  of  diminishing  its 
calibre. 

The  trachea  is  covered  externally  by  a  tough,  fibre-elastic  membrane, 
and  internally  by  mucous  membrane,  lined  by  columnar  ciliated  epithelial 
cells.  The  cilia  are  always  waving  from  within  outward.  When  the  two 
bronchi  enter  the  lungs  they  divide  and  subdivide  into  numerous  and 
smaller  branches,  which  penetrate  the  lung  in  every  direction  until  they 
finally  terminate  in  the  pulmonary  lobules. 

As  the  bronchial  tubes  become  smaller  their  walls  become  thinner ;  the 
cartilaginous  rings  disappear,  but  are  replaced  by  irregular  angular  plates 
of  cartilage;  when  the  tube  becomes  less  than  the  ^  of  an  inch  in  di- 
ameter they  wholly  disappear,  and  the  fibrous  and  mucous  coats  blend 
together,  forming  a  delicate,  elastic  membrane,  with  circular  muscular  fibres. 

The  Lungs  occupy  the  cavity  of  the 
thorax,  are  conical  in  shape,  of  a  pink 
color  and  a  spongy  texture.  They  are 
composed  of  a  great  number  of  distract 
lobules,  the  pulmonary  lobules  >  con- 
nected together  by  interlobular  con- 
nective tissue.  These  lobules  vary  in 
size,  are  of  an  oblong  shape,  and  are 
composed  of  the  ultimate  ramifications 
of  the  bronchial  tubes,  within  which  are 
contained  the  air  vesicles  or  cells.  The 
walls  of  the  air  vesicles,  exceedingly 
thin  and  delicate,  are  lined  internally  by 
a  layer  of  tessellated  epithelium,  exter- 
nally covered  by  elastic  fibres,  which 
give  the  lungs  their  elasticity  and  dis- 
tensibility. 

The  Venous  Blood  is  distributed  to 
the  lungs  for  aeration  by  the  pulmonary 
artery,  the  terminal  branches  of  which 
form  a  rich  plexus  of  capillary  vesssls 
surrounding  the  air  cells;  the  air  and 

blood  are  thus  brought  into  intimate  relationship,  being  separated  only  by 

the  delicate  walls  of  the  air  cells  and  capillaries. 


The 


Diagram  of  the  respiratory  organs. 

"he  windpipe  leading  down  from  th 
larynx  is  seen  to  branch  into  tw 
large  bronchi,  which  subdivide  after 
they  enter  their  respective  lungs. 


the 
wo 


RESPIRATION.  61 

The  thoracic  cavity  in  which  the  respiratory  organs  are  lodged  is  of  a 
conical  shape,  having  its  apex  directed  upward,  its  base  downward.  Its 
framework  is  formed  posteriorly  by  the  spinal  column,  anteriorly  by  the 
sternum,  and  laterally  by  the  ribs  and  costal  cartilages.  Between  and  over 
the  ribs  lie  muscles,  fascia  and  skin ;  above  the  thorax  is  completely  closed 
by  the  structures  passing  into  it  and  by  the  cervical  fascia  and  skin ;  below 
it  is  closed  by  the  diaphragm.  It  is  therefore  an  air-tight  cavity. 

The  Pleura.  Each  lung  is  surrounded  by  a  closed  serous  membrane, 
the  pleura,  one  layer  of  which,  the  visceral,  is  reflected  over  the  lung,  the 
other,  the  parietal,  reflected  over  the  wall  of  the  thorax ;  between  the  two 
layers  is  a  small  amount  of  fluid  which  prevents  friction  during  the  play  of 
the  lungs  in  respiration. 

Owing  to  the  elastic  tissue  which  is  present  in  the  lungs,  they  are  very 
readily  distensible,  so  much  so,  indeed,  that  the  pressure  of  the  air  inside 
the  trachea  and  lungs  is  sufficient  to  distend  them  until  they  completely 
fill  all  parts  of  the  thoracic  cavity  not  occupied  by  the  heart  and  great 
vessels.  The  elastic  tissue  endows  them  not  only  with  distensibility, 
but  also  with  the  power  of  elastic  recoil,  by  which  they  are  enabled 
to  accommodate  themselves  to  all  variations  in  the  size  of  the  thoracic 
cavity. 

When  the  chest  walls  recede,  the  air  within  the  lungs  expands  and 
presses  them  against  the  ribs;  when  the  chest  walls  contract,  the  air 
being  driven  out,  the  elastic  tissue  recoils  and  the  lungs  return  to  their 
original  condition.  The  movements  of  the  lungs  are  therefore  entirely 
passive. 

As  the  capacity  of  the  chest  in  a  state  of  rest  is  greater  than  the  volume 
of  the  lungs  after  they  are  collapsed,  it  is  quite  evident  that  in  the  living 
condition  the  lungs  are  distended  and  in  a  state  of  elastic  tension,  which 
is  greater  or  less  in  proportion  as  the  thoracic  cavity  is  increased  or  dimin- 
ished in  size.  The  elastic  tissue,  always  on  the  stretch,  is  endeavoring  to 
pull  the  visceral  layer  of  the  pleura  away  from  the  parietal  layer,  but  is 
antagonized  by  the  pressure  of  the  air  within  the  air  passages.  This  con- 
dition of  things  persists  as  long  as  the  thoracic  cavity  remains  air  tight ;  but 
if  an  opening  be  made  in  the  thoracic  wall,  the  pressure  of  the  external  air 
which  was  previously  supported  by  the  practically  rigid  walls  of  the  thorax 
now  presses  upon  the  lung  with  as  much  force  as  the  air  within  the  lung. 
The  two  pressures  being  neutralized,  there  is  nothing  to  prevent  the  elastic 
tissue  from  recoiling,  driving  the  air  out  and  collapsing.  The  elastic  ten- 
sion of  the  lungs  can  be  readily  measured  in  man  after  death  by  inserting 


62  HUMAN  PHYSIOLOGY. 

a  manometer  into  the  trachea.  Upon  opening  the  thorax  and  allowing  the 
tissue  to  recoil,  the  air  presses  upon  the  mercury  and  elevates  it,  the  extent 
to  which  it  is  raised  being  the  index  of  the  pressure.  Hutchinson  calcu- 
lated the  pressure  to  be  one-half  pound  to  the  square  inch  of  the  lung 
surface. 

Respiratory  movements.  The  movements  of  respiration  are  two,  and 
consist  of  an  alternate  dilatation  and  contraction  of  the  chest,  known  as 
inspiration  and  expiration. 

1.  Inspiration  is  an  active  process,  the  result  of  the  expansion  of  the 
thorax,  whereby  air  is  introduced  into  the  lungs. 

2.  Expiration  is  a  partially  passive  process,  the  result  of  the  recoil  of 
the  elastic  walls  of  the  thorax,  and  the  recoil  of  the  elastic  tissue  of  the 
lungs,  whereby  the  carbonic  acid  is  expelled. 

In  Inspiration  the  chest  is  enlarged  by  an  increase  in  all  its  diameters 
viz. : — 

1.  The  vertical  is  increased  by  the  contraction  and  descent  of  the  dia- 
phragm when  it  approximates  a  straight  line. 

2.  The  antero-posterior  and  transverse  diameters  are  increased  by  the 
elvation  and  rotation  of  the  ribs  upon  their  axes. 

In  ordinary  tranquil  inspiration  the  muscles  which  elevate  the  ribs  and 
thrust  the  sternum  forward,  and  so  increase  the  diameters  of  the  chest,  are 
the  external  inter costals,  running  from  above  downward  and  forward,  the 
sternal  portion  of  the  internal  intercostah  and  the  levatores  costarum. 

In  the  extraordinary  efforts  of  inspiration  certain  auxiliary  muscles  are 
brought  into  play,  viz. :  the  sterno-mastoid,  pectorales,  serratus  magnus, 
which  increase  the  capacity  of  the  thorax  to  its  utmost  limit. 

In  Expiration  the  diameters  of  the  chest  are  all  diminished,  viz. : 

1 .  The  vertical,  by  the  ascent  of  the  diaphragm. 

2.  The  antero-posterior,  by  a  depression  of  the  ribs  and  sternum. 

In  ordinary  tranquil  expiration  the  diameters  of  the  thorax  are  dimin- 
ished by  the  recoil  of  the  elastic  tissue  of  the  lungs  and  the  ribs;  but  in 
forcible  expiration  the  muscles  which  depress  the  ribs  and  sternum,  and 
thus  further  diminish  the  diameter  of  the  chest,  are  the  internal  inter  costals, 
the  infracostal*,  and  the  triangularis  sterni. 

In  the  extraordinary  efforts  of  expiration  certain  auxiliary  muscles  are 
brought  into  plaj,  viz.:  the  abdominal  and  sacro-lumbalis  muscles,  which 
diminish  the  capacity  of  the  thorax  to  its  utmost  limit. 

Expiration  is  aided  by  the  recoil  of  the  elastic  tissue  of  the  lungs  and  ribs 
and  the  pressure  of  the  air. 


RESPIRATION.  63 

Movements  of  the  Glottis.  At  each  inspiration  the  rima-glottidis  is 
dilated  by  a  separation  of  the  vocal  cords,  produced  by  the  contraction  of 
the  crico-arytenoid  muscles,  so  as  to  freely  admit  the  passage  of  air  into  the 
lungs :  in  expiration  they  fall  passively,  together,  but  do  not  interfere  with 
the  exit  of  air  from  the  chest. 

Nervous  Mechanism  of  Respiration.  The  movements  of  Respira- 
tory muscles,  though  capable  of  being  modified  to  a  certain  extent  by 
efforts  of  the  will,  are  of  an  automatic  character,  and  called  forth  by 
nervous  impulses  emanating  from  the  medulla  oblongata.  The  Respiratory 
centre,  the  so-called  vital  point,  generates  the  nerve  impulses,  which,  travel- 
ing outward  through  the  phrenic  and  intercostal  nerves,  excite  contractions 
of  the  diaphragm  and  intercostal  muscles  respectively.  This  centre  is  for 
the  most  part  automatic  in  its  action,  though  it  is  capable  of  being  modified 
by  impulses  reflected  to  it  through  various  sensory  nerves. 

This  centre  may  be  stimulated  — 

1.  Directly ',  by  the  condition  of  the  blood.     An  increase  of  carbonic  acid 
or  a  diminution  of  oxygen  in  the  blood  causes  an  acceleration  of  the  respi- 
ratory movements;  the  reverse  of  these  conditions  causes  a  diminution  of 
the  respiratory  movements. 

2.  Indirectly,  by  reflex  action.     The  medulla  may  be  excited  to  action 
through  the  pneumogastric  nerve,  by  the  presence  of  carbonic  acid  in  the 
lungs  irritating  its  terminal  filaments ;  through  the  fifth  nerve,  by  irritation 
of  the  terminal  branches;  and  through  the  nerves  of  general  sensibility.     In 
either  case  this  centre  reflects  motor  impulses  to  the  respiratory  muscles 
through  the  phrenic,  intercostals,  inferior  laryngeal  and  other  nerves. 

Types  of  Respiration.  The  abdominal  type  is  most  marked  in  young 
children,  irrespective  of  sex ;  the  respiratory  movements  being  effected  by 
the  diaphragm  and  abdominal  muscles. 

In  the  superior  costal  type,  exhibited  by  the  adult  female,  the  respiratory 
movements  are  more  marked  in  the  upper  part  of  the  chest,  from  the  1st  to 
the  yth  ribs,  permitting  the  uterus  to  ascend  in  the  abdomen  during  preg- 
nancy without  interfering  with  respiration. 

In  the  inferior  costal  type,  manifested  by  the  male,  the  movements  are 
largely  produced  by  the  muscles  of  the  lower  portion  of  the  chest,  from  the 
7th  rib  downward,  assisted  by  the  diaphragm. 

The  respiratory  movements  vary  according  to  age,  sleep  arid  exercise, 
being  most  frequent  in  early  life,  but  averaging  20  per  minute  in  adult  life. 
They  are  diminished  by  sleep  and  increased  by  exercise.  There  are  about 
four  pulsations  of  the  heart  to  each  respiratory  act. 


64  HUMAN  PHYSIOLOGY. 

During  inspiration  two  sounds  are  produced;  the  one,  heard  in  the 
thorax,  in  the  trachea  and  larger  bronchial  tubes,  is  tubular  in  character; 
the  other,  heard  in  the  substance  of  the  lungs,  is  vesiciilar  in  character. 

AMOUNT  OF  AIR   EXCHANGED  IN  RESPIRATION,  AND  CAPACITY 
OF  LUNGS. 

The  Tidal  or  breathing  volume  of  air,  that  which  passes  in  and  out  of  the 
lungs  at  each  inspiration  and  expiration,  is  estimated  at  from  20  to  30  cubic 
inches. 

The  Complemental  air  is  that  amount  which  can  be  taken  into  the  lungs 
by  a  forced  inspiration,  in  addition  to  the  ordinary  tidal  volume,  and 
amounts  to  about  no  cubic  inches. 

The  Reserve  air  is  that  which  usually  remains  in  the  chest  after  the  ordi- 
nary efforts  of  expiration,  but  which  can  be  expelled  by  forcible  expiration. 
The  volume  of  reserve  air  is  about  100  cubic  inches. 

The  Residual  air  is  that  portion  which  remains  in  the  chest  and  cannot 
be  expelled  after  the  most  forcible  expiratory  efforts,  and  which  amounts, 
according  to  Dr.  Hutchinson,  to  about  100  cubic  inches. 

The  Vital  Capacity  of  the  chest  indicates  the  amount  of  air  that  can 
be  forcibly  expelled  from  the  lungs  after  the  deepest  possible  inspiration, 
and  is  an  index  of  an  individual's  power  of  breathing  in  disease  and  pro- 
longed severe  exercise.  The  combined  amounts  of  the  tidal,  the  comple- 
mental  and  reserve  air,  230  cubic  inches,  represents  the  vital  capacity  of  an 
individual  5  feet  7  inches  in  height.  The  vital  capacity  varies  chiefly  with 
stature.  It  is  increased  8  cubic  inches  for  every  inch  in  height  above  this 
standard,  and  diminishes  8  cubic  inches  for  each  inch  below  it. 

The  Tidal  Volume  of  air  is  carried  only  into  the  trachea  and  larger 
bronchial  tubes  by  the.  inspiratory  movements.  It  reaches  the  deeper 
portions  of  the  lungs  in  obedience  to  the  law  of  diffusion  of  gases,  which  is 
inversely  proportionate  to  the  square  root  of  their  densities. 

The  ciliary  action  of  the  columnar  cells  lining  the  bronchial  tubes  also 
assists  in  the  interchange  of  air  and  carbonic  acid. 

The  entire  volume  of  air  passing  in  and  out  of  the  thorax  in  24  hours  is. 
subject  to  great  variation,  but  can  be  readily  estimated  from  the  tidal 
volume  and  the  number  of  respirations  per  minute.  Assuming  that  an 
individual  takes  into  the  chest  20  cubic  inches  at  each  inspiration,  and 
breathes  18  times  per  minute,  in  24  hours  there  would  pass  in  and  out  of 
the  lungs  518,400  cubic  inches,  or  300  cubic  feet. 

Chemistry  of  Respiration.     As  the  inspired  air  undergoes  a  change 


RESPIRATION.  65 

in  composition  during  its  stay  in  the  lungs  which  renders  it  unfit  for  further 
respiration,  it  becomes  requisite,  for  the  correct  understanding  of  respiration, 
to  ascertain  the  composition  of  both  inspired  and  expired  air. 

Composition  of  Air.  Chemical  analysis  has  shown  that  every  100 
vols.  of  air  contains  20.81  vols.  of  oxygen,  and  70.19  vols.  of  nitrogen,  and 
0.03  vol.  of  carbonic  acid.  Aqueous  vapor  is  also  present,  though  the 
quantity  is  variable.  The  higher  the  temperature  the  greater  the  amount. 

The  changes  in  the  air  effected  by  respiration  are — 

Loss  of  oxygen,  to  the  extent  of  5  cubic  inches  per  100  of  air,  or  i  in  20. 
Gain  of  carbonic  acid,  to  the  extent  of  4.66  cubic  inches  per  100  of 

air  or  .93  inch  in  20. 

Increase  of  water  vapor  and  organic  matter. 
Elevation  of  temperature. 
Increase  and  at  times  decrease  of  nitrogen. 
Gain  of  ammonia. 

The  total  qtiantity  of  oxygen  withdrawn  from  the  air  and  consumed  by 
the  body  in  24  hours  amounts  to  15  cubic  feet,  and  can  be  readily  esti- 
mated from  the  amount  consumed  at  each  respiration.  Assuming  that  one 
inch  of  oxygen  remains  in  the  lungs  at  each  respiration,  in  one  hour  there 
are  consumed  1080  inches,  and  in  24  hours,  25,920  cubic  inches  or  15  cubic 
feet,  weighing  18  oz.  To  obtain  this  quantity,  300  cubic  feet  of  air  are 
necessary. 

The  quantity  of  oxygen  consumed  daily  is  subject  to  considerable  varia- 
tion. It  is  increased  by  exercise,  digestion  and  lowered  temperature,  and 
decreased  by  the  opposite  conditions. 

The  quantity  of  carbonic  acid  exhaled  in  24  hours  varies  greatly.  It 
can  be  estimated  in  the  same  way.  Assuming  that  an  individual  exhales 
•93  ~f-  cubic  inch  at  each  respiration,  in  one  hour  there  are  eliminated  1008 
cubic  inches,  and  in  24  hours,  24.192  cubic  inches  or  14  cubic  feet,  contain- 
ing 7  ozs.  of  pure  carbon. 

The  exhalation  of  carbonic  acid  is  increased  by  muscular  exercise ; 
nitrogenous  food ;  tea,  coffee  and  rice;  age,  and  by  muscular  development ; 
decreased  by  a  lowering  of  temperature ;  repose ;  gin  and  brandy,  and  a. 
dry  condition  of  the  air. 

As  there  is  always  more  oxygen  consumed  than  carbonic  acid  exhaled, 
and  as  oxygen  unites  with  carbon  to  form  an  equal  volume  of  carbonic  acid, 
it  is  evident  that  a  certain  quantity  of  oxygen  disappears  within  the  body. 
In  all  probability  it  unites  with  the  sulphur  hydrogen  of  the  food  to  form 
water. 


66  HUMAN   PHYSIOLOGY. 

The  amount  of  watery  vapor  which  passes  out  of  the  body  with  the 
expired  air  amounts  to  from  one  to  two  pounds. 

The  organic  matter,  though  slight  in  amount,  gives  the  odor  to  the  breath. 
In  a  room  with  defective  ventilation,  the  organic  matter  accumulates  and 
gives  rise  to  headache,  nausea,  drowsiness,  etc.  Long  continued  breathing 
of  such  air  produces  general  ill  health.  It  is  not  so  much  the  presence  of 
CO2  in  increased  amount,  as  the  presence  of  organic  matter  which  neces- 
sitates thorough  ventilation. 

Condition  of  the  Gases  in  the  Blood. 

Oxygen  is  absorbed  from  the  lungs  into  the  arterial  blood  by  the  coloring 
matter,  hemoglobin,  with  which  it  exists  in  a  state  of  loose  combination, 
and  is  disengaged  during  the  process  of  nutrition. 

Carbonic  acid,  arising  in  the  tissues,  is  absorbed  into  the  blood,  in  conse- 
quence of  its  alkalinity,  where  it  exists  in  a  state  of  simple  solution  and 
also  in  a  state  of  feeble  combination  with  the  carbonates,  soda  and  potassa, 
forming  the  bi'carbonates. 

Nitrogen  is  simply  held  in  solution  in  the  plasma. 

Exchange  of  Gases  in  the  Air  Cells.  From  the  difference  in  tension 
of  the  oxygen  in  the  air  cells  (27.44  mm.  of  Hg),  and  of  the  oxygen  in  the 
venous  blood  (22  mm.  Hg),  and  of  the  difference  of  the  carbonic  acid  tension 
in  the  venous  blood  (41  mm.  Hg),  and  in  the  air  cells  (27  mm.  Hg),  it  might 
be  concluded  that  the  passage  of  the  gases  might  be  due  solely  to  pressure. 
The  absorption  of  oxygen,  however,  does  not  follow  absolutely  the  law  of 
pressures ;  that  chemical  processes  are  involved  is  shown  by  the  union  of 
oxygen  with  the  haemoglobin  of  the  blood  corpuscles.  The  exhalation  of 
CO 2  is  also  partly  a  chemical  process,  as  it  has  been  shown  that  the  quan- 
tity excreted  is  greatly  increased  when  oxygen  is  simultaneously  absorbed. 
Oxygen  not  only  favors  the  exhalation  of  loosely  combined  CO2,  but  favors 
the  expulsion  of  that  which  can  only  be  excreted  by  the  addition  of  acids 
to  the  blood. 

Changes  in  the  Blood  during  Respiration. 

As  the  blood  passes  through  the  lungs  it  is  changed  in  color,  from  the 
dark  purple  hue  of  venous  blood  to  the  bright  red  scarlet  of  arterial 
blood. 

The  heterogeneous  composition  of  venous  blood  is  exchanged  for  the 
uniform  composition  of  the  arterial. 

It  gains  oxygen  and  loses  carbonic  acid. 

Its  coagulability  is  increased.     Temperature  is  diminished. 

Asphyxia.     If  the  supply  of  oxygen  to  the  lungs  be  diminished  and 


ANIMAL  HEAT.  67 

the  carbonic  acid  retained  in  the  blood,  the  normal  respiratory  movements 
cease,  the  condition  of  asphyxia  ensues,  which  soon  terminates  in  death. 

The  phenomena  of  asphyxia  are,  violent  spasmodic  action  of  the  respi- 
ratory muscles,  attended  by  convulsions  of  the  muscles  of  the  extremities, 
engorgement  of  the  venous  system,  lividity  of  the  skin,  abolition  of  sensi- 
bility and  reflex  action,  and  death. 

The  cause  of  death  is  a  paralysis  of  the  heart,  from  over  distention  by 
blood.  The  passage  of  the  blood  through  the  capillaries  is  prevented  by 
contraction  of  the  smaller  arteries,  from  irritation  of  the  vasomotor  centre. 
The  heart  is  enfeebled  by  a  want  of  oxygen  and  inhibited  in  its  action  by 
the  inhibitory  centres. 


ANIMAL  HEAT. 

The  Functional  Activity  of  all  the  organs  and  tissues  of  the  body  is 
attended  by  the  evolution  of  heat,  which  is  independent,  for  the  most  part, 
of  external  conditions.  Heat  is  a  necessary  condition  for  the  due  perform- 
ance of  all  vital  actions ;  though  the  body  constantly  loses  heat  by  radia- 
tion and  evaporation,  it  possesses  the  capability  of  renewing  it  and  main- 
taining it  at  a  fixed  standard.  The  normal  temperature  of  the  body  in  the 
adult,  as  shown  by  means  of  a  delicate  thermometer  placed  in  the  axilla, 
ranges  from  97.25°  Fahr.  to  99.5°  Fahr.,  though  the  mean  normal  tem- 
perature is  estimated  by  Wunderlich  at  98.6°  Fahr. 

The  temperature  varies  in  different  portions  of  the  body,  according  to 
the  degree  in  which  oxidation  takes  place ;  being  the  highest  in  the  muscles 
during  exercise,  in  the  brain,  blood,  liver,  etc. 

The  conditions  which  produce  variations  in  the  normal  temperature 
of  the  body  are :  age,  period  of  the  day,  exercise,  food  and  drink,  climate, 
season  and  disease. 

Age.  At  birth  the  temperature  of  the  infant  is  about  i°  F.  above  that  of 
the  adult,  but  in  a  few  hours  falls  to  95.5°  F.,  to  be  followed  in  the  course 
of  24  hours  by  a  rise  to  the  normal  or  a  degree  beyond.  During  childhood 
the  temperature  approaches  that  of  the  adult ;  in  aged  persons  the  tempera- 
ture remains  about  the  same,  though  they  are  not  as  capable  of  resisting 
the  depressing  effects  of  external  cold  as  adults.  A  diurnal  variation  of 
the  temperature  occurs  from  1.8°  F.  to  3.6°  F.  (Jiirgensen);  the  maximum 
occurring  late  in  the  afternoon,  from  4  to  9  p.  M.,  the  minimum^  early  in 
the  morning,  from  I  to  7  A.  M. 

Exercise.     The  temperature  is  raised  from   i°  to  2°  F.  during  active 


68  HUMAN   PHYSIOLOGY. 

contractions  of  the  muscular  masses,  and  is  probably  due"  to  the  increased 
activity  of  chemical  changes ;  a  rise  beyond  this  point  being  prevented  by 
its  diffusion  to  the  surface,  consequent  on  a  more  rapid  circulation,  radia- 
tion, more  rapid  breathing,  etc. 

Food  and  drink.  The  ingestion  of  a  hearty  meal  increases  the  tempera- 
ture but  slightly;  an  absence  of  food,  as  in  starvation,  produces  a  marked 
decrease.  Alcoholic  drinks,  in  large  amounts,  in  persons  unaccustomed 
to  their  use,  cause  a  depression  of  the  temperature,  amounting  from  i°  to 
2°  F.  Tea  causes  a  slight  elevation. 

External  temperature.  Long  continued  exposure  to  cold,  especially  if 
the  body  is  at  rest,  diminishes  the  temperature  from  i°  to  2°  F.,  while 
exposure  to  a  great  heat  slightly  increases  it. 

Disease  frequently  causes  a  marked  variation  in  the  normal  temperature 
of  the  body,  rising  as  high  as  107°  F.  in  typhoid  fever,  and  105°  F.  in 
pneumonia;  in  cholera  it  falls  as  low  as  80°  F.  Death  usually  occurs 
when  the  heat  remains  high  and  persistent,  from  106°  to  110°  F. ;  the 
increase  of  heat  in  disease  is  due  to  excessive  production  rather  than  to 
diminished  elimination. 

The  source  of  heat  is  to  be  sought  for  in  the  chemical  decompositions 
and  hydrations  taking  place  during  the  general  process  of  nutrition,  and  the 
combustion  of  the  carbonaceous  compounds  by  the  oxygen  of  the  inspired 
air;  the  amount  of  its  production  is  in  proportion  to  the  activity  of  the 
internal  changes. 

Every  contraction  of  a  muscle,  every  act  of  secretion,  each  exhibition 
of  nerve  force,  is  accompanied  by  a  change  in  the  chemical  composition  of 
the  tissues  and  an  evolution  of  heat.  The  reduction  of  the  disintegrated 
tissues  to  their  simplest  form  by  oxidation ;  the  combination  of  the  oxygen 
of  the  inspired  air  with  the  carbon  and  hydrogen  of  the  blood  and  tissues, 
results  in  the  formation  of  carbonic  acid  and  water  and  the  generation  of  a 
large  amount  of  heat. 

Certain  elements  of  the  food,  particularly  the  non-nitrogenized  substances, 
undergo  oxidation  without  taking  part  in  the  formation  of  the  tissues,  being 
transformed  into  carbonic  acid  and  water,  and  thus  increase  the  sum  of 
heat  in  the  body. 

Heat-producing  Tissues.  All  the  tissues  of  the  body  add  to  the 
general  amount  of  heat,  according  to  the  degree  of  their  activity.  But 
special  structures  on  account  of  their  mass  and  the  large  amount  of  blood 
they  receive,  are  particularly  to  be  regarded  as  heat  producers  ;  e.  g.  : — 

I.  During  mental    activity  the  brain    receives    nearly  one-fifth    of  the 


SECRETION.  69 

entire  volume  of  blood,  and  the  venous  blood  returning  from  it  is  charged 
with  waste  matters,  and  its  temperature  is  increased. 

2.  The  muscular  tissue,  on  account  of  the  many  chemical  changes  occur- 
ring during    active    contractions,    must   be   regarded   as    the    chief  heat- 
producing  tissue. 

3.  The  secreting  glands,  during  their  functional  activity,  add  largely  to 
the  amount  of  heat. 

The  entire  quantity  of  heat  generated  within  the  body  has  been  demon- 
strated experimentally  to  be  about  2300  calories,  a  calorie  or  heat  unit 
being  that  amount  of  heat  required  to  raise  the  temperature  of  one  kilo,  of 
water  (2.2  Ibs.)  one  degree  Centigrade.  This  quantity  of  heat  if  not  utilized 
and  retained  within  the  body  would  elevate  its  temperature  in  24  hours 
about  60°  F.  That  this  volume  of  heat  depends  very  largely  upon  the 
oxidation  of  the  food  stuffs  can  be  shown  experimentally. 

The  normal  temperature  of  the  body  is  maintained  by  a  constant  expen- 
diture of  the  heat  in  several  directions : — 

1.  In  warming  the  food,  drink  and  air  tfcat  are  consumed  in  24  hours. 
For  this  purpose  about  157  heat  units  are  required. 

2.  In  evaporating  water  from  the  skin  and  lungs;  619  heat  units  being 
utilized  for  this  purpose. 

3.  In  radiation  and  conduction.     By  these  processes  the  body  loses  at 
least  50  per  cent,  of  its  heat,  or  1156  heat  units. 

4.  In  the  production  of  work ;  the  work  of  the  circulatory,  respiratory, 
muscular,  and  nervous  apparatus  being  performed  by  the  transformation  of 
369  heat  units  into  units  of  work. 

The  nervous  system  influences  the  production  of  heat  in  a  part,  by 
increasing  the  amount  of  blood  going  through  it  by  its  action  upon  the 
vasomotor  nerves.  Whether  there  exists  a  special  heat  centre  has  not 
been  satisfactorily  determined,  though  this  is  probable. 


SECRETION. 

The  Process  of  Secretion  consists  in  the  separation  of  materials  from 
the  blood  which  are  either  to  be  again  utilized  to  fulfill  some  special  pur- 
pose in  the  economy,  or  are  to  be  removed  from  the  body  as  excrementi- 
tious  matter ;  in  the  former  case  they  constitute  the  secretions,  in  the  latter, 
the  excretions. 

The  materials  which  enter  into  the  composition  of  the  secretions  are 
derived  from  the  nutritive  principles  of  the  blood,  and  require  special 


70  HUMAN  PHYSIOLOGY. 

organs,  <?.  £•.,  gastric  glands,  mammary  glands,  etc.,  for  their .  proper 
elaboration. 

The  materials  which  compose  the  excretions  preexist  in  the  blood,  and 
are  the  results  of  the  activities  of  the  nutritive  process;  if  retained  within 
the  body  they  exert  a  deleterious  influence  upon  the  composition  of  the 
blood. 

Destruction  of  a  secreting  gland  abolishes  the  secretion  peculiar  to  it, 
and  it  cannot  be  formed  by  any  other  gland;  but  among  the  excreting 
organs  there  exists  a  complementary  relation,  so  that  if  the  function  of  one 
organ  be  interfered  with,  another  performs  it  to  a  certain  extent. 

CLASSIFICATION  OF  THE  SECRETIONS. 
PERMANENT   FLUIDS. 

Serous  fluids.  Vitreous  humor  of  the  eye. 

Synovial  fluid.  Fluid  of  the  labyrinth  of  the  internal 

Aqueous  humor  of  the  eye.  .  ear. 

•  Cerebro-spinal  fluid. 

TRANSITORY   FLUIDS. 

Mucus.  Gastric  juice. 

Sebaceous  matter.  Pancreatic  juice. 

Cerumen  (external  meatus).  Secretion  from  Brunner's  glands. 

Meibomian  fluid.  Secretion  from  Leiberkiihn's  glands. 

Milk  and  colostrum.  Secretions  from  follicles  of  the  large 

Tears.  intestine. 

Saliva.  Bile  (also  an  excretion). 

EXCRETIONS. 

Perspiration  and  the  secretion  of        Urine. 

the  axillary  glands.  Bile  (also  a  secretion). 

FLUIDS    CONTAINING    FORMED   ANATOMICAL   ELEMENTS. 

Seminal  fluid,  containing  spermatozoids.     Fluid  of  the  Graafian  follicles. 

The  essential  apparatus  for  secretion  is  a  delicate,  homogeneous, 
structureless  membrane,  on  one  side  of  which,  in  close  contact,  is  a  capil- 
lary plexus  of  blood  vessels,  and  on  the  other  side  a  layer  of  cells  whose 
physiological  function  varies  in  different  situations. 

Secreting  organs  may  be  divided  into  membranes  and  glands. 

Serous  membranes  usually  exist  as  closed  sacs,  the  inner  surface  of  which 
is  covered  by  pale,  nucleated  epithelium,  containing  a  small  amount  of 
secretion. 


SECRETIONS.  71 

The  serous  membranes  are  the  pleura, peritoneum, pericardium,  synovial 
sacs,  etc. 

The  serous  ftiiids  are  of  a  pale  amber  color,  somewhat  viscid,  alkaline, 
coagulable  by  heat,  and  resemble  the  serum  of  the  blood;  their  amount 
is  but  small;  the  pleural  varies  from  4  to  7  drachms;  the  peritoneal  from 
I  to  4  ounces  ;  the  pericardial  from  I  to  3  drachms. 

The  synovial  fluid  is  colorless,  alkaline,  and  extremely  viscid,  from  the 
presence  of  synovine. 

The  function  of  serous  fluids  is  to  moisten  the  opposing  surfaces,  so  as- to 
prevent  friction  during  the  play  of  the  viscera. 

The  mucous  membranes  are  soft  and  velvety  in  character,  and  line  the 
cavities  and  passages  leading  to  the  exterior  of  the  body,  e.g.,  the  gastro- 
intestinal, pulmonary  and  genito-urinary.  They  consist  of  a  primary 
basement  membrane  covered  with  epithelial  cells,  which  in  some  situations 
are  tessellated,  in  others,  columnar. 

Mucus  is  a  pale,  semi-transparent,  alkaline  fluid,  containing  epithelial 
cells  and  leucocytes.  It  is  composed,  chemically,  of  water,  an  albuminous 
principle,  mucosine,  and  mineral  salts;  the  principal  varieties  are  nasal, 
bronchial,  vaginal  and  urinary. 

Secreting  Glands  are  formed  of  the  same  elements  as  the  secreting 
membranes;  but  instead  of  presenting  flat  surfaces,  are  involuted,  forming 
tubules,  which  may  be  simple  follicles,  e.g.,  mucous,  uterine  or  intestinal; 
or  compoiind  follicles,  e.g.,  gastric  glands,  mammary  glands ;  or  racemose 
glands,  e.g.,  salivary  glands  and  pancreas.  They  are  composed  of  a  base- 
ment membrane,  enveloped  by  a  plexus  of  blood  vessels,  and  are  lined  by 
epithelial  and  true  secreting  cells,  which  in  different  glands  possess  the 
capability  of  elaborating  elements  characteristic  of  their  secretions. 

In  the  production  of  the  secretions  tveo  essentially  different  processes 
are  concerned  : — 

1.  Chemical.     The  formation  and  elaboration  of  the  characteristic  organic 
ingredients   of  the   secreted   fluids,   e.g.,  pepsin,  pancreatin,  takes    place 
during  the  intervals  of  glandular  activity,  as  a  part  of  the  general  function 
of  nutrition.     They  are  formed  by  the  cells  lining  the  glands,  and  can  often 
be  seen  in  their  interior  with  the  aid  of  the  microscope,  e.g.,  bile  in  the 
liver  cells,  fat  in  the  cells  of  the  mammary  gland. 

2.  Physical.     Consisting  of  a  transudation  of  water  and  mineral  salts 
from  the  blood  into  the  interior  of  the  gland. 

During  the  intervals  of  glandular  activity,  only  that  amount  of  blood 
passes  through  the  gland  sufficient  for  proper  nutrition ;  when  the  gland 


72  HUMAN    PHYSIOLOGY. 

begins  to  secrete,  under  the  influence  of  an  appropriate  stimulus,  the  blood 
vessels  dilate  and  the  quantity  of  blood  becomes  greatly  increased  beyond 
that  flowing  through  the  gland  during  its  repose. 

Under  these  conditions  a  transudation  of  water  and  salts  takes  place, 
washing  out  the  characteristic  ingredients,  which  are  discharged  by  the 
gland  ducts.  The  discharge  of  the  secretions  is  intermittent;  they  are 
retained  in  the  glands  until  they  receive  the  appropriate  stimulus,  when 
they  pass  into  the  larger  ducts  by  the  vis-a-tergo,  and  are  then  discharged 
by  the  contraction  of  the  muscular  walls  of  the  ducts. 

The  activity  of  glandular  secretion  is  hastened  by  an  increase  in  the 
blood  pressure  and  retarded  by  a  diminution. 

The  nervous  centres  in  the  medulla  oblongata  influence  secretion,  (i)  by 
increasing  or  diminishing  the  amount  of  blood  entering  a  gland  ;  (2)  by 
exerting  a  direct  influence  upon  the  secreting  cells  themselves,  the  centres 
being  excited  by  reflex  irritation,  mental  emotion,  etc. 

MAMMARY  GLANDS. 

The  Mammary  Glands  secrete  the  milk,  and  undergo  at  different 
periods  of  life  remarkable  changes  in  structure.  Though  rudimentary  in 
childhood,  they  gradually  increase  in  size  as  the  young  female  approaches 
puberty. 

The  gland  presents,  at  its  convexity,  a  small  prominence  of  skin,  the 
nipple,  surrounded  by  an  areola  of  a  deeper  tint.  It  is  covered  anteriorly 
by  a  layer  of  adipose  tissue  and  posteriorly  by  a  fibrous  structure  which 
attaches  it  loosely  to  the  pectoralis  muscle. 

During  utero-gestation  the  mammae  become  large,  firm,  well-developed 
and  lobulated ;  the  areola  becomes  darker  and  the  veins  more  prominent. 
In  the  intervals  of  lactation  *  the  glands  gradually  sink  in  size  to  their 
original  condition,  undergo  involution,  and  become  non-secreting  organs. 

Structure  of  the  Mammae.  The  mamma  is  a  conglomerate  gland, 
consisting  of  a  number  of  lobes,  from  15  to  20  in  number,  each  of  which 
is  subdivided  into  lobules  made  up  of  gland  vesicles  or  acini.  The  ducts 
which  convey  the  secretion  to  the  exterior,  the  lactiferous  ducts,  open  by 
15  to  20  orifices  upon  the  surface  of  the  nipple,  at  the  base  of  which  they 
are  dilated  to  form  little  reservoirs  in  which  the  milk  collects  during  the 
periods  of  active  secretion. 

The  walls  of  the  lacteal  duct  consist  of  white,  fibrous  tissue,  and  non- 
striated  muscular  fibres,  lined  by  short  columnar  cells,  which  disappear 
during  active  lactation.  The  ducts  measure  about  the  ^  of  an  inch  in 


MILK.  73 

diameter;  as  they  pass  into  the  substance  of  the  gland,  each  duct  divides 
into  a  number  of  branches,  which  are  distributed  to  distinct  lobules  and 
terminate  in  the  acini. 

An  acinus  is  made  up  of  a  number  of  vesicles  composed  of  a  homoge- 
neous membrane,  lined  by  pavement  epithelium.  The  gland  vesicles  are 
held  together  by  white,  fibrous  tissue,  which  unites  the  lobules  into  lobes. 


MILK. 

Milk  has  a  pale  blue  color,  is  almost  inodorous,  of  a  sweetish  taste,  an 
alkaline  reaction,  and  a  specific  gravity  varying  from  1.025  to  1-046. 
Examined  microscopically  it  is  seen  to  contain  an  immense  number  of 
globules,  measuring  the  1Q^g^  of  an  inch  in  diameter,  suspended  in  a  clear 
fluid ;  these  are  the  milk  globules,  formed  of  a  small  mass  of  oily  matter 
covered  by  a  layer  of  albumin. 

The  quantity  of  milk  secreted  by  the  human  female  in  24  hours,  during 
the  period  of  lactation,  is  about  two  to  three  pints ;  the  quantity  removed  by 
the  infant  from  a  full  breast  at  one  time  being  about  two  ounces. 

COMPOSITION  OF  MILK. 

Water, 890.00 

Proteids,  including  casein  and  serum  albumin,  .    .    .  35.00 

Fatty  matter  (butter), 25.00 

Sugar  (lactose)  with  extractives, 48.00 

Salts, 2.00 


Casein  is  the  nutritive  principle  of  milk,  and  constitutes  its  most  important 
ingredient.  It  is  held  in  solution  by  an  alkali,  but  upon  the  addition  of  an 
acid  it  undergoes  coagulation,  passing  into  a  semi-solid  form.  The  presence 
of  lactic  acid,  resulting  from  a  transformation  of  milk  sugar,  causes  spon- 
taneous coagulation  to  take  place. 

The  Fatty  matter  is  more  or  less  solid  at  ordinary  temperature,  and  con- 
sists of  margarine  and  oleine ;  when  subjected  to  the  churning  process  the 
globules  run  together  and  form  a  coherent  mass,  the  butter. 

When  milk  is  allowed  to  stand  for  a  varying  length  of  time,  the  fat 
globules  rise  to  the  surface,  forming  a  layer  more  or  less  thickr  the  cream. 

Milk  sugar  or  lactose  is  an  important  ingredient  in  the  food  of  the  young 
child ;  it  is  readily  transformed  into  lactic  acid  in  the  presence  of  nitrogen- 
ized  ferments. 

F 


74  HUMAN   PHYSIOLOGY. 

Influences  modifying  the  secretion.  During  lactation  there  is  a 
demand  for  an  increased  amount  of  fluid,  and  if  not  supplied,  the  amount 
of  milk  secreted  is  diminished.  Good  food  in  sufficient  quantity  is  neces- 
sary for  the  proper  elaboration  of  milk,  though  no  particular  article  influ- 
ences its  production. 

Mental  emotion  at  times  influences  the  character  of  the  milk,  decreasing 
the  amount  of  its  different  constituents. 

Mechanism  of  Secretion.  The  water  and  salts  preexist  in  the  blood 
and  pass  into  the  gland  vesicles  by  osmosis.  The  casein,  fatty  matter  and 
sugar  appear  only  in  the  mammary  gland,  but  the  mechanism  of  their 
formation  is  not  understood. 

Colostrum  is  a  yellowish,  opaque  fluid,  formed  in  the  mammary  glands 
toward  the  latter  period  of  utero-gestation ;  it  consists  of  water,  albumin, 
fat,  sugar  and  salts,  and  acts  as  a  laxative  to  the  newly-born  infant. 


VASCULAR  OR  DUCTLESS  GLANDS. 

The  Vascular  Glands  are  regarded  as  possessing  the  power  of  acting 
upon  certain  elements  of  the  food  and  aiding  the  process  of  sanguinifica- 
tion;  of  modifying  the  composition  of  the  blood  as  it  flows  through  their 
substance,  by  some  act  of  secretion. 

The  vascular  glands  are  the  spleen,  supra-renal  capsules,  thyroid  and 
thymiis  glands. 

The  Spleen  is  about  5  inches  in  length,  6  ounces  in  weight,  of  a  dark 
bluish  color,  and  situated  in  the  left  hypochondriac  region.  It  is  covered 
externally  by  a  reflection  of  the  peritoneum,  beneath  which  is  the  proper 
fibrous  coat,  composed  of  areolar  and  elastic  tissue  and  non-striated  muscu- 
lar fibres.  From  the  inner  surface  of  the  fibrous  envelope  processes  or  tra- 
beculae  are  given  off,  which  penetrate  the  substance  of  the  gland,  forming  a 
network,  in  the  meshes  of  which  is  contained  the  spleen  pulp.  The  splenic 
artery  divides  into  a  number  of  branches,  some  of  which,  when  they  become 
very  minute,  pass  directly  into  veins,  while  others  terminate  in  true  capillaries. 

As  the  capillary  vessels  ramify  through  the  substance  of  the  gland,  their 
walls  frequently  disappear  and  the  blood  passes  from  the  arteries  into  the 
veins  through  lacuna  (Gray). 

The  splenic  or  Malpighian  corpuscles  are  small  bodies,  spherical  or 
ovoid  in  shape,  the  -fa  of  an  inch  in  diameter,  situated  upon  the  sheaths  of 
the  small  arteries.  They  consist  of  a  delicate  membrane,  containing  a 


VASCULAR   OR   DUCTLESS   GLANDS.  75 

semi-fluid  substance  composed  of  numerous  small  cells  resembling  lymph 
corpuscles.  The  spleen  pulp  is  a  dark  red,  semi-fluid  substance,  of  a  soft 
consistence,  contained  in  the  meshes  of  the  trabeculae.  In  it  are  found 
numerous  corpuscles,  like  those  observed  in  the  Malpighian  bodies,  blood 
corpuscles  in  a  natural  and  altered  condition,  nuclei  and  pigment  granules. 
Function  of  the  Spleen,  Probably  influences  the  preparation  of  the 
albuminous  food  for  nutrition ;  during  digestion  the  spleen  becomes  larger, 
its  contents  are  increased  in  amount,  and  after  digestion  it  gradually  dimin- 
ishes in  size,  returning  to  the  normal  condition. 

The  red  corpuscles  are  here  disintegrated,  after  having  fulfilled  their 
function  in  the  blood ;  the  splenic  venous  blood  containing  relatively  a 
small  quantity. 

The  white  corpuscles  appear  to  be  increased  in  number,  the  blood  of  the 
splenic  vein  containing  an  unusually  large  proportion. 

The  spleen  serves  also  as  a  reservoir  for  blood  when  the  portal  circula- 
tion becomes  obstructed. 

The  nervous  system  controls  the  enlargement  of  the  spleen ;  division  of 
the  nerve  produces  dilatation  of  the  vessels,  stimulation  contracts  them. 

The  Supra-renal  Capsules  are  triangular,  flattened  bodies,  situated 
above  the  kidney.  They  are  invested  by  a  fibrous  capsule  sending  in 
trabeculse,  forming  the  framework.  The  glandular  tissue  is  composed  of 
two  portions,  a  cortical  and  medullary.  The  cortical  being  made  up  of 
small  cylinders  lined  by  cells  and  containing  an  opaque  mass,  nuclei  and 
granular  matter.  The  medullary  consists  of  a  fibrous  network  containing 
in  the  alveoli  nucleated  protoplasm. 

The  Thyroid  gland  consists  of  a  fibrous  stroma,  containing  ovoid 
closed  sacs,  measuring  on  the  average  ^  of  an  inch,  formed  of  a  delicate 
membrane  lined  by  cells;  the  contents  of  the  sacs  consist  of  yellowish 
albuminous  fluid. 

The  Thymus  gland  is  most  developed  in  early  life  and  almost  disap- 
pears in  the  adult.  It  is  divided  by  processes  of  fibrous  tissue  into  lobules, 
and  these  again  into  follicles  which  contain  lymphoid  corpuscles. 

The  functions  of  ttie  vascular  organs  appear  to  be  the  more  complete 
elaboration  of  the  blood  necessary  for  proper  nutrition ;  they  are  most  highly 
developed  during  infancy  and  embryonic  life,  when  growth  and  develop- 
ment are  most  active. 


76  HUMAN   PHYSIOLOGY. 

EXCRETION. 

The  Principal  Excrementitious  Fluids  discharged  from  the  body 
are  the  urine,  perspiration  and  bile;  they  hold  in  solution  principles  of 
waste  which  are  generated  during  the  activity  of  the  nutritive  process,  and 
are  the  ultimate  forms  to  which  the  organic  constituents  are  reduced  in  the 
body.  They  also  contain  inorganic  salts. 

The  Urinary  Apparatus  consists  of  the  kidneys,  ureters  and  bladder. 


KIDNEYS. 

The  Kidneys  are  the  organs  for  the  secretion  of  urine;  they  resemble 
a  bean  in  shape,  are  from  four  to  five  inches  in  length,  two  in  breadth,  and 
weigh  from  four  to  six  ounces. 

They  are  situated  in  the  lumbar  region,  one  on  each  side  of  the  vertebral 
column,  behind  the  peritoneum,  and  extend  from  the  nth  rib  to  the  crest 
of  the  ilium ;  the  anterior  surface  is  convex,  the  posterior  surface  concave, 
the  latter  presenting  a  deep  notch,  the  hilus. 

The  kidney  is  surrounded  by  a  thin,  smooth  membrane  composed  of 
white  fibrous  and  yellow  elastic  tissue ;  though  it  is  attached  to  the  surface 
of  the  kidney  by  minute  processes  of  connective  tissue  it  can  be  readily  torn 
away.  The  substance  of  the  kidney  is  dense  but  friable. 

Upon  making  a  longitudinal  section  of  the  kidney  it  will  be  observed 
that  the  hilus  extends  into  the  interior  of  the  organ  and  expands  to  form 
a  cavity  known  as  the  sinus.  This  cavity  is  occupied  by  the  upper 
dilated  portion  of  the  ureter,  the  interior  of  which  forms  the  pelvis. 
The  ureter  subdivides  into  several  portions,  which  ultimately  give  origin 
to  a  number  of  smaller  tubes  termed  calyces,  which  receive  the  apices  of 
the  pyramids. 

The  Parenchyma  of  the  Kidney  consists  of  two  portions,  viz  : — 

1.  An  internal  Q\  medullary  portion,  consisting  of  a  series  of  pyramids 
or  cones,  some  twelve  or  fifteen  in   number.     They  present  a  distinctly  stri- 
ated appearance,  a  condition  due  to  the  straight  direction  of  the  tubules  and 
blood  vessels. 

2.  An  external  or  cortical  portion,  consisting  of  a  delicate  matrix  con- 
taining an   immense   number   of  tubules   having   a  markedly  convoluted 
appearance.     Throughout   its  structure   are    found   numerous  small  ovoid 
bodies -termed  Malpighian  corpuscles. 


KIDNEYS. 


77 


The  Uriniferous  Tubules.     Tr/e  kidney  is  a  compound  tubular  gland 
composed  of  microscopic  tubules,  whose  function  it  is  to  secrete  from  the 


FIG.  9. 


LONGITUDINAL   SECTION   THROUGH    THE    KIDNEY,   THE   PELVIS    OF   THE    KIDNEY,  AND    A 
NUMBER   OF    RENAL   CALYCES. 

A,  branch  of  the  renal  artery;  U,  ureter;  C,  renal  calyx;  i,  cortex;  i',  medullary 
rays  ;  i",  labyrinth,  or  cortex  proper  ;  2,  medulla  ;  2',  papillary  portion  of  medulla, 
or  medulla  proper;  2",  border  layer  of  the  medulla;  3,  3,  transverse  section  through 
the  axes  of  the  tubules  of  the  border  layer ;  4,  fat  of  the  renal  sinus  ;  5,  5,  arterial 
branches ;  *,  transversely  coursing  medulla  rays. —  Tyson,  after  Henle. 


blood  those  waste  products  which  collectively  constitute  the  urine.     If  the 
apex  of  each,  pyramid  be  examined  with  a  lens,  it  will  present  a  number 


78 


HUMAN  PHYSIOLOGY. 


FIG.  10. 


of.  small  orifices  which   are   the   beginnings   of  the    uriniferous  tubules. 

From  this  point  the  tubules  pass  outward  in  a  straight  but  somewhat 
diverging  manner  toward  the  cortex,  giving  off  at 
acute  angles  a  number  of  branches  (Fig.  10).  From 
the  apex  to  the  base  of  the  pyramids  they  are 
known  as  the  tubules  of  Bellini.  In  the  cortical 
portion  of  the  kidney  each  tubule  becomes  en- 
larged and  twisted,  and  after  pursuing  an  extremely 
convoluted  course,  turns  backward  into  the  medul- 
lary portion  for  some  distance,  forming  the  descend- 
ing limb  of  Henle's  loop;  it  then  turns  upon  itself, 
forming  the  ascending  limb  of  the  loop,  reenters 
the  cortex,  again  expands,  and  finally  terminates  in 
a  spherical  enlargement  known  as  Mailer's  or  Bow- 
man's capsule.  Within  this  capsule  is  contained  a 
small  tuft  of  blood  vessels  constituting  the  glomerulus 
or  Malpighian  corpuscle. 

Structure  of  the  Tubules.  Each  tubule  consists 
of  a  basement  membrane  lined  by  epithelial  cells 
throughout  its  entire  exetnt.  The  tubule  and  its 
contained  epithelium  vary  in  shape  and  size  in  different 
parts  of  its  course.  The  termination  of  the  convoluted 

.    tube  consists  of  a  little  sac  or  capsule,  which  is  ovoidal 
Diagrammatic    exposi- 
tion  of  the  method  in  shape  and  measures  about  ^^  of  an  inch  in  size. 

rouft'ilbes^unufro"  This  capsule  is  lined  by  a  layer  of  flattened  epithelial 

form  primitive  cones    ceus  which  is  also  reflected  over  the  surface  of  the 

—  lyson.)  after  L,ud- 

ivig.  glomerulus.     During  the  periods  of  secretory  activity, 

the  blood  vessels  of  the  glomerulus  become  filled  with 
blood,  so  that  the  cavity  of  the  sac  is  almost  obliterated;  after  secretory 
activity  the  blood  vessels  contract  and  the  sac  cavity  becomes  enlarged. 
In  that  portion  of  the  tubule  lying  between  the  capsule  and  Henle's  loop 
the  epithelial  cells  are  cuboidal  in  shape ;  in  Henle's  loop  they  are  flattened, 
while  in  the  remainder  of  the  tubule  they  are  cuboidal  and  columnar. 

Blood  vessels  of  the  Kidney.  The  renal  artery  is  of  large  size  and 
enters  the  organ  at  the  hilum;  it  divides  into  several  large  branches,  which 
penetrate  the  substance  of  the  kidney,  between  the  pyramids,  at  the  base 
of  which  they  form  an  anastomosing  plexus,  which  completely  surrounds 
them.  From  this  plexus  vessels  follow  the  straight  tubes  toward  the  apex, 
while  others,  entering  the  cortical  portion,  divide  into  small  twigs  which 


KIDNEYS.  79 

enter  the  Malpighian  body  and  form  a  mass  of  convoluted  vessels,  the 
glomerulus.  After  circulating  through  the  Malpighian  tuft,  the  blood  is 
gathered  together  by  two  or  three  small  veins,  which  again  subdivide  and 
form  a  fine  capillary  plexus,  which  envelops  the  convoluted  tubules;  from 
this  plexus  the  veins  converge  to  form  the  emulgent  vein,  which  empties 
into  the  vena  cava. 

The  nerves  of  the  kidney  follow  the  course  of  the  blood  vessels  and 
are  derived  from  the  renal  plexus. 

The  Ureter  is  a  membranous  tube,  situated  behind  the  peritoneum, 
about  the  diameter  of  a  goose  quill,  1 8  inches  in  length,  and  extends  from 
the  pelvis  of  the  kidney  to  the  base  of  the  bladder,  which  it  perforates  in 
an  oblique  direction.  It  is  composed  of  3  coats,  fibrous,  muscular  and 
mucous. 

The  Bladder  is  a  reservoir  for  the  temporary  reception  of  the  urine 
prior  to  its  expulsion  from  the  body;  when  fully  distended  it  is  ovoid  in 
shape,  and  holds  about  one  pint.  It  is  composed  of  four  coats,  serous, 
muscular,  the  fibres  of  which  are  arranged  longitudinally  and  circularly, 
areolar  and  mucotts.  The  orifice  of  the  bladder  is  controlled  by  the 
sphincter  vesicce,  a  muscular  band  about  half  an  inch  in  width. 

As  soon  as  the  urine  is  formed  it  passes  through  the  tubuli  uriniferi 
into  the  pelvis,  and  from  thence  through  the  ureters  into  the  bladder,  which 
it  enters  at  an  irregular  rate.  Shortly  after  a  meal,  after  the  ingestion  of 
large  quantities  of  fluid,  and  after  exercise,  the  urine  flows  into  the  blad- 
der quite  rapidly,  while  it  is  reduced  to  a  few  drops  during  the  intervals  of 
digestion.  It  is  prevented  from  regurgitating  into  the  ureters  on  account  of 
the  oblique  direction  they  take  between  the  mucous  and  muscular  coats. 

Nervous  Mechanism  of  Urination.  When  the  urine  has  passed  into 
the  bladder,  it  is  there  retained  by  the  sphincter  vesicae  muscle,  kept  in  a 
state  of  tonic  contraction  by  the  action  of  a  nerve  centre  in  the  lumbar 
region  of  the  spinal  cord.  This  centre  can  be  inhibited  and  the  sphincter 
relaxed,  either  reflexly,  by  impressions  coming  through  sensory  nerves  from 
the  mucous  membrane  of  the  bladder,  or  directly,  by  a  voluntary  impulse 
descending  the  spinal  cord.  When  the  desire  to  urinate  is  experienced, 
impressions  made  upon  the  vesical  sensory  nerves  are  carried  to  the  centres 
governing  the  sphincter  and  detrusor  urines  muscles  and  to  the  brain.  If 
now  the  act  of  urination  is  to  take  place,  a  voluntary  impulse,  originating 
in  the  brain,  passes  down  the  spinal  cord  and  still  further  inhibits  the 
sphincter  vesicee  centre,  with  the  effect  of  relaxing  the  muscle,  and  of 
stimulating  the  centre  governing  the  detrusor  muscle,  with  the  effect  of  con- 


80  HUMAN   PHYSIOLOGY. 

trading  the  muscle  and  expelling  the  urine.  If  the  act  is  to  be  sup- 
pressed, voluntary  impulses  inhibit  the  detrtisor  centre  and  possibly  stimu- 
late the  sphincter  centre.  * 

The  genito-  spinal  centre  controlling  these  movements  is  situated  in  that 
portion  of  th'e  spinal  cord  corresponding  to  the  origin  of  the  3d,  4th  and 
5th  sacral  nerves. 

URINE. 

Normal  Urine  is  of  a  pale  yellow  or  amber  color,  perfectly  transparent, 
with  an  aromatic  odor,  an  acid  reaction,  a  specific  gravity  of  1.020,  and  a 
temperature  when  first  discharged  of  100°  Fahr. 

The  color  varies  considerably  in  health,  from  a  pale  yellow  to  a  brown 
hue,  due  to  the  presence  of  the  coloring  matter,  urobilin  or  urochrome. 

The  transparency  is  diminished  by  the  presence  of  mucus,  the  calcium 
and  magnesium  phosphates  and  the  mixed  urates. 

The  reaction  of  the  urine  is  acid,  owing  to  the  presence  of  acid  phos- 
phate  of  sodium.     The   degree    of  acidity,  however,  varies   at   different 
periods  of  the  day.     Urine  passed  in  the  morning  is  strongly  acid,  while 
that  passed  during  and  after  digestion,  especially  if  the  food  is  largely  vege- 
table in  character,  is  either  neutral  or  alkaline. 
The  specific  gravity  varies  from  1.015  to  1.025. 

The  quantity  of  urine  excreted  in  24  hours  is  between  40  and  50  fluid 
ounces,  but  ranges  above  and  below  this  standard. 

The  odor  is  characteristic,  and  caused  by  the  presence  of  taurylic  and  phe- 
nylic  acids,  but  is  influenced  by  vegetable  foods  and  other  substances  elimi- 
nated by  the  kidneys. 

COMPOSITION  OF  URINE. 
Water,      .....................  967. 

Urea,    ......................     14-230 

Other  nitrogenized  crystalline  bodies,  uric  acid,  prin- 

cipally in  the  form  of  alkaline  urates. 
Creatin,  creatinin,  xanthin,  hypoxanthin. 
Hippuric   acid,  leucin,  tyrosin,  taurin,  cystin,  all  in   f 

small  amounts,  and  not  constant. 
Mucus  and  pigment. 
Salts  :— 
/  Inorganic,   principally   sodium   and    potassium   sul-  "] 

phates,  phosphates  and  chlorides,  with  magnesium 
I        and   calcium   phosphates,   traces   of  silicates   and  K 

V      chlorides. 

\Organic  :    lactates,    hippurates,    acetates,    formates, 
i    whiclTappear  only  occasionally. 
Sugar,     ...................    ..a  trace. 

Gases  (nitrogen  and  carbonic  acid  principally). 


looo.oo 


URINE.  81 

The  Average  Quantity  of  the  principal  constituents  excreted  in  24 
hours  is  as  follows : — 

Water, 52  fluid  oz. 

Urea, 512.4  grains. 

Uric  acid, "8.5 

Phosphoric  acid, 45.0 

Sulphuric  acid, 31.11 

Inorganic  salts, 323.25 

Lime  and  magnesia, 6.5 

To  Determine  the  amount  of  solid  matters  in  any  given  amount  of 
urine,  multiply  the  last  two  figures  of  the  specific  gravity  by  the  coefficient 
of  Heeser,  2.33;  e.  g.,  in  1000  grains  of  urine  having  a  specific  gravity 
i. 022,  there  are  contained  22  X  2-33  =  S1-2^  grains  of  solid  matter. 

Organic  Constituents  of  Urine.  Urea  is  one  of  the  most  important 
of  the  organic  constituents  of  the  urine,  and  is  present  to  the  extent  of  from 
2.5  to  3.2  per  cent.  Urea  is  a  colorless,  neutral  substance,  crystallizing  to 
four-sided  prisms  terminated  by  oblique  surfaces.  When  crystallization  is 
caused  to  take  place  rapidly,  the  crystals  take  the  form  of  long,  silky 
needles.  Urea  is  soluble  in  water  and  alcohol;  when  subjected  to  pro- 
longed boiling  it  is  decomposed,  giving  rise  to  carbonate  of  ammonia.  In 
the  alkaline  fermentation  of  urine,  urea  takes  up  two  molecules  of  water 
with  the  production  of  carbonate  of  ammonia. 

The  average  amount  of  urea  excreted  daily  has  been  estimated  at  about 
500  grains.  As  urea  is  one  of  the  principal  products  of  the  breaking  up  of 
the  albuminous  compounds  within  the  body,  it  is  quite  evident  that  the 
quantity  produced  and  eliminated  in  24  hours  will  be  increased  by  any 
increase  in  the  amount  of  albuminous  food  consumed,  by  a  rapid  destruc- 
tion of  albuminous  tissues,  as  is  witnessed  in  various  pathological  states,  in- 
anition, febrile  conditions,  fevers,  etc.  A  farinaceous  or  vegetable  diet  will 
diminish  the  urea  production  nearly  one-half. 

Muscular  exercise  when  the  nutrition  of  the  body  is  in  a  state  of  equi- 
librium does  not  seem  to  increase  the  quantity  of  urea. 

Seat  of  Urea  Formation.  As  to  the  seat  of  urea  formation,  little 
is  positively  known.  It  is  quite  certain  that  it  preexists  in  the  blood  and  is 
merely  excreted  by  the  kidneys.  It  is  not  produced  in  muscles,  as  even 
after  prolonged  exercise  hardly  a  trace  of  urea  is  to  be  found  in  them. 
Experimental  and  pathological  facts  point  to  the  liver  as  the  probable  organ 
engaged  in  urea  formation.  Acute  yellow  atrophy  of  the  liver,  suppurative 
diseases  of  the  liver  diminish  almost  entirely  the  production  of  urea. 


82  HUMAN    PHYSIOLOGY. 

Uric  acid  is  also  a  constant  ingredient  of  the  urine  and  is  closely  allied 
to  urea.  It  is  a  nitrogenized  substance,  carrying  out  of  the  body  a  large 
quantity  of  nitrogen.  The  amount  eliminated  daily  varies  from  5  to  10 
grains.  Uric  acid  is  a  colorless  crystal  belonging  to  the  rhombic  system. 
It  is  insoluble  in  water,  and  if  eliminated  in  excessive  amounts  it  is  de- 
po-ited  as  a  "  brick-red  "  sediment  in  the  urine.  It  is  doubtful  if  uric  acid 
exists  in  a  free  state,  being  combined  for  the  most  part  with  sodium  and 
potassium  bases  forming  urates.  It  is  to  be  regarded  as  one  of  the  termi- 
nal products  of  the  disassimilation  of  albuminous  compounds,  and  is  prob- 
ably produced  in  the  liver. 

Hippuric  acid  is  found  very  generally  in  urine,  though  it  is  present 
only  in  small  amounts.  It  is  increased  by  a  diet  of  asparagus,  cranberries, 
plums  and  by  the  administration  of  benzoic  and  cinnamic  acids.  It  is 
probably  formed  in  the  kidney. 

Kreatinin  resembles  the  kreatin  derived  from  muscles.  It  is  a  colorless 
crystal,  belonging  to  the  rhombic  system.  Its  origin  is  unknown,  though  it 
is  largely  increased  in  amount  by  albuminous  food.  About  15  grains  are 
excreted  daily. 

Xanthin,  Sarkin,  Oxaluric  Acid  and  Allantoin  are  also  constituents 
of  urine.  They  are  nitrogenized  compounds  and  are  also  terminal  products 
of  albuminous  compounds. 

Urobilin,  the  coloring  matter  of  the  urine,  is  a  derivative  of  the  bile  pig- 
ments. It  is  particularly  abundant  in  febrile  conditions,  giving  to  the  urine 
its  reddish- yellow  color. 

Inorganic  Constituents  of  Urine.  Earthy  Phosphate.  Phos- 
phoric acid  in  combination  with  magnesium  and  calcium  is  excreted  daily 
to  the  extent  of  from  15  to  30  grains.  The  phosphates  are  insoluble  in 
water,  but  are  held  in  solution  in  the  urine  by  its  acid  ingredients,  alkalinity 
of  the  urine  being  attended  with  a  copious  precipitation  of  the  phosphates. 
Mental  work  increases  the  amount  of  phosphoric  acid  excreted,  a  condition 
caused  by  increased  metabolism  of  the  nervous  tissue. 

Sulphuric  acid  in  combination  with  sodium  and  potassium  constitute  the 
sulphates,  of  which  about  30  grains  are  excreted  daily.  Sulphuric  acid 
results  largely  from  the  decomposition  of  albuminous  food  and  from 
increased  destruction  of  animal  tissues. 

The  Gases  of  the  urine  are  carbonic  acid  and  nitrogen. 

Mechanism  of  Urinary  Secretion.  As  the  kidney  anatomically  pre- 
sents an  apparatus  for  filtration  (the  Malpighian  bodies),  and  an  apparatus 


LIVER.  83 

for  secretion  (the  epithelial  cells  of  the  urinary  tubules),  it  might  be  inferred 
that  the  elimination  of  the  constituents  of  the  urine  is  accomplished  by  the 
twofold  process  of  filtration  and  secretion;  that  the  water  and  highly 
diffusible  inorganic  salts  simply  pass  by  diffusion  through  the  walls  of  the 
blood  vessels  of  the  glomerulus  into  the  capsule  of  Miiller,  while  the  urea 
and  remaining  organic  constituents  are  removed  by  true  secretory  action  of 
the  renal  epithelium.  Modern  experimentation  supports  this  view  of  renal 
action. 

The  secretion  of  urine  is  therefore  partly  physical  and  partly  vital. 

The  Filtration  of  urinary  constituents  from  the  glomerulus  into  Miiller's 
capsule  depends  largely  upon  the  blood  pressure  and  the  rapidity  of  blood 
flow  in  the  renal  artery  and  glomerulus.  Among  the  influences  which 
increase  the  pressure  and  velocity,  may  be  mentioned  increased  frequency 
and  force  of  the  heart's  action,  contraction  of  the  capillary  vessels  of  the 
body  generally,  dilatation  of  the  renal  artery,  increase  in  the  volume  of  the 
blood. 

The  reverse  conditions  lower  the  blood  pressure  and  diminish  the  secre- 
tion of  urine. 

The  elimination  of  the  organic  matters  by  secretory  activity  of  the  renal 
epithelium  seems  to  be  well  established  by  modern  experiments.  These 
substances,  removed  from  the  blood  in  the  secondary  capillary  plexus  of 
blood  vessels,  by  a  true  selective  action  of  the  epithelium,  are  dissolved  and 
washed  toward  the  pelvis  by  the  liquid  coming  from  the  capsules. 

The  blood  supply  to  the  kidney  is  regulated  by  the  nervous  system.  If 
the  renal  nerves  be  divided,  the  renal  artery  dilates  and  a  copious  flow  of 
urine  takes  place.  If  the  peripheral  ends  of  the  same  nerves  be  stimulated, 
the  artery  contracts  and  the  urinary  flow  ceases.  The  same  is  true  of  the 
splanchnic  nerves,  through  which  the  vasomotor  nerves  coming  from  the 
medulla  oblongata  and  spinal  cord  pass  to  the  renal  plexus. 


LIVER. 

The  Liver  is  a  highly  vascular,  conglomerate  gland,  appended  to  the 
alimentary  canal.  It  is  the  largest  gland  in  the  body,  weighing  about  4^ 
pounds ;  it  is  situated  in  the  right  hypochondriac  region,  and  retained  in 
position  by  five  ligaments,  four  of  which  are  formed  by  duplicatures  of  the 
peritoneal  investment. 

The  proper  coat  of  the  liver  is  a  thin  but  firm  fibrous  membrane,  closely 
adherent  to  the  surface  of  the  organ,  which  it  penetrates  at  the  transverse 


84  HUMAN   PHYSIOLOGY. 

fissure,  and  follows  the  vessels  in  their  ramifications  through  its  substance, 
constituting  Glissorfs  capsule. 

Structure  of  the  Liver.  The  liver  is  made  up  of  a  large  number  of 
small  bodies,  the  lobules,  rounded  or  ovoid  in  shape,  measuring  the  -fa  of 
an  inch  in  diameter,  separated  by  a  space  in  which  are  situated  blood 
vessels,  nerves,  hepatic  ducts  and  lymphatics. 

The  lobules  are  composed  of  cells,  which,  when  examined  microscopi- 
cally, exhibit  a  rounded  or  polygonal  shape,  and  measure,  on  the  average, 
the  I^OQ  of  an  inch  in  diameter;  they  possess  one,  and  at  times  two,  nuclei; 
they  also  contain  globules  of  fat,  pigment  matter,  and  animal  starch.  The 
cells  constitute  the  secreting  structure  of  the  liver,  and  are  the  true  hepatic 
cells. 

The  Blood  vessels  which  enter  the  liver  are  (i)  The  portal  vein, 
made  up  of  the  gastric,  splenic,  superior  and  inferior  mesenteric  veins ;  (2) 
the  hepatic  artery,  a  branch  of  the  coeliac  axis ;  both  of  which  are  invested 
by  a  sheath  of  areolar  tissue ;  the  vessels  which  leave  the  liver  are  the 
hepatic  veins,  originating  in  its  interior,  collecting  the  blood  distributed  by 
the  portal  vein  and  hepatic  artery,  and  conducting  it  to  the  ascending  vena 
cava. 

Distribution  of  Vessels.  The  portal  vein  and  hepatic  artery,  upon 
entering  the  liver,  penetrate  its  substance,  divide  into  smaller  and  smaller 
branches,  occupy  the  spaces  between  the  lobules,  completely  surrounding 
and  limiting  them,  and  constitute  the  interlobular  vessels.  The  hepatic 
artery,  in  its  course,  gives  off  branches  to  the  walls  of  the  portal  vein  and 
Glisson's  capsule,  and  finally  empties  into  the  small  branches  of  the  portal 
vein  in  the  interlobular  spaces. 

The  interlobular  vessels  form  a  rich  plexus  around  the  lobules,  from 
which  branches  pass  to  neighboring  lobules  and  enter  their  substance, 
where  they  form  a  very  fine  network  of  capillary  vessels,  ramifying  over 
the  hepatic  cells,  in  which  the  various  functions  of  the  liver  are  performed. 
The  blood  is  then  collected  by  small  veins,  converging  toward  the  centre 
of  the  lobule,  to  form  the  intralobular  vein,  which  runs  through  its  long 
axis  and  empties  into  the  sub-lobular  vein.  The  hepatic  veins  are  formed 
by  the  union  of  the  sub-lobular  veins,  and  carry  the  blood  to  the  ascending 
vena  cava;  their  walls  are  thin  and  adherent  to  the  substance  of  the 
hepatic  tissue. 

The  Hepatic  Ducts  or  Bile  Capillaries  originate  within  the  lobules, 
in  a  very  fine  plexus  lying  between  the  hepatic  cells ;  whether  the  smallest 
vessels  have  distinct  membranous  walls,  or  whether  they  originate  in  the 


LIVER.  85 

spaces  between  the  cells  by  open  orifices,  has  not  been  satisfactorily  deter- 
mined. 

The  Bile  Channels  empty  into  the  interlobular  ducts,  which  measure 
about  suVff  °f  an  mcn  m  diameter,  and  are  composed  of  a  thin  homogeneous 
membrane  lined  by  flattened  epithelial  cells. 

As  the  interlobular  bile  ducts  unite  to  form  larger  trunks,  they  receive 
an  external  coat  of  fibrous  tissue,  which  strengthens  their  walls;  they 
finally  unite  to  form  one  large  duct,  the  hepatic  duct,  which  joins  the  cystic 
duct ;  the  union  of  the  two  forms  the  ductus  communis  choledochus,  which 
is  about  three  inches  in  length,  the  size  of  a  goose  quill,  and  opens  into  the 
duodenum. 

The  Gall  Bladder  is  a  pear-shaped  sack,  about  four  inches  in  length, 
situated  in  a  fossa  on  the  under  surface  of  the  liver.  It  is  a  reservoir  for 
the  bile,  and  is  capable  of  holding  about  one  ounce  and  a  half  of  fluid.  It 
is  composed  of  three  coats,  (l)  serous,  a  reflection  of  the  peritoneum,  (2) 
fibrous  and  muscular,  (3)  mucous. 

Functions  of  the  Liver.  The  liver  is  a  complex  organ  having  a 
variety  of  relations  to  the  general  processes  of  the  body.  While  its  physio- 
logical actions  are  not  yet  wholly  understood,  it  may  be  said  that  it — 

1.  Secretes  bile. 

2.  Forms  glycogen. 

3.  Assists  in  the  formation  of  urea  and  allied  products. 

4.  Modifies  the  composition  of  the  blood  as  it  passes  through  it.     . 

The  Secretion  of  Bile.  The  characteristic  constituents  of  the  bile  do 
not  preexist  in  the  blood,  but  are  formed  within  the  interior  of  the  liver 
cells  out  of  materials  derived  from  the  venous  and  arterial  blood.  The 
hepatic  cells  absorbing  these'materials  elaborate  them  into  bile  elements;  and 
in  so  doing  undergo  histological  changes  similar  to  those  exhibited  by  other 
secretory  glands.  The  bile  once  formed,  it  passes  into  the  mouths  of 
the  bile  capillaries,  near  the  periphery  of  the  lobules.  Under  the  influence 
of  the  vis-a-tergo  of  the  new  formed  bile  it  flows  from  the  smaller  into  the 
larger  bile  ducts,  and  finally  empties  into  the  intestine,  or  is  regurgitated 
into  the  gall  bladder,  where  it  is  stored  up  until  it  is  required  for  the 
digestive  process  in  the  small  intestine.  The  study  of  the  secretion  of  bile 
by  means  of  biliary  fistulae  reveals  the  facts  that  the  secretion  is  continuous 
and  not  intermittent ;  that  the  hepatic  cells  are  constantly  pouring  bile  into 
the  ducts  which  convey  it  into  the  gall  bladder.  As  this  fluid  is  required 
only  during  intestinal  digestion,  it  is  only  then  that  the  walls  of  the  gall 
bladder  contract  and  discharge  it  into  the  intestine. 


86  HUMAN   PHYSIOLOGY. 

The  flow  of  bile  from  the  liver  cells  into  the  gall  bladder  is  accomplished 
by  the  inspiratory  movements  of  the  diaphragm,  the  contraction  of  the  mus- 
cular fibres  of  the  biliary  ducts,  as  well  as  the  vis-a-tergo  of  new  formed 
bile.  Any  obstacle  to  the  outflow  of  bile  into  the  intestine  leads  to  an  accu- 
mulation within  the  bile  ducts.  The  pressure  within  the  ducts  increasing 
beyond  that  of  the  blood  within  the  capillaries,  a  re  absorption  of  biliary 
matters  by  the  lymphatics  takes  place,  giving  rise  to  the  phenomena  of 
jaundice. 

The  Bile  is  both  a  secretion  and  an  excretion  ;  it  contains  new  constitu- 
ents which  are  formed  only  in  the  substance  of  the  liver,  and  are  destined 
to  play  an  important  part  ultimately  in  nutrition  ;  it  contains  also  waste 
ingredients  which  are  discharged  into  the  intestinal  canal  and  eliminated 
from  the  body. 

Glycogenic  Function.  In  addition  to  the  preceding  function,  Ber- 
nard, in  1848,  demonstrated  the  fact  that  the  liver,  during  life,  normally 
produces  a  sugar-forming  substance,  analogous  in  its  chemical  composition 
to  starch,  which  he  terms  glycogen  ;  also  that  when  the  liver  is  removed 
from  the  body,  and  its  blood  vessels  thoroughly  washed  out,  after  a  few 
hours  sugar  again  makes  its  appearance,  in  abundance. 

It  can  be  shown  to  exist  in  the  blood  of  the  hepatic  vein  as  well  as  in  a 
decoction  of  the  liver  substance,  by  means  of  either  Trommer's  or  Fehling's 
tests,  even  when  the  blood  of  the  portal  vein  does  not  contain  a  trace  of 
sugar. 

Origin  and  Destination  of  Glycogen.  Glycogen  appears  to  be 
formed  de  novo  in  the  liver  cells,  from  materials  derived  from  the  food, 
whether  the  diet  be  animal  or  vegetable,  though  a  larger  per  cent,  is 
formed  when  the  animal  is  fed  on  starchy  and  saccharine,  than  when  fed  on 
animal  food.  The  glucose,  which  is  one  of  the  products  of  digestion,  is 
absorbed  by  the  blood  vessels,  and  carried  directly  into  the  liver  ;  as  it  does 
not  appear  in  the  urine,  as  it  would  if  injected  at  once  into  the  general  cir- 
culation, it  is  probable  that  it  is  detained  in  the  liver,  dehydrated  and  stored 
up  as  glycogen.  The  change  is  shown  by  the  following  formula  :  — 

Glucose.      Water.        Glycogen. 

C2H1206-H20  = 


The  glycogen  thus  formed  is  stored  up  in  the  hepatic  cells  for  the  future 
requirements  of  the  system.  When  it  is  carried  from  the  liver  it  is  again 
transformed  into  glucose  by  the  agency  of  a  ferment.  Glycogen  does  not 
undergo  oxidation  in  the  blood  ;  this  takes  place  in  the  tissues,  particularly 


LIVER.  87 

in  the  muscles,  where  it  generates  heat  and  contributes  to  the  development 
of  muscular  force. 

Glycogen,  when  obtained  from  the  liver,  is  an  amorphous,  starch-like 
substance,  of  a  white  color,  tasteless  and  colorless,  and  soluble  in  water;  by 
boiling  with  dilute  acids,  or  subjected  to  the  action  of  an  animal  ferment, 
it  is  easily  converted  into  glucose.  When  an  excess  of  sugar  is  generated 
by  the  liver,  it  can  be  found,  not  only  in  the  blood  of  the  hepatic  vein, 
but  also  in  other  portions  of  the  body;  under  these  circumstances  it  is 
eliminated  by  the  kidneys,  appearing  in  the  urine,  constituting  the  condition 
of  glycosuria. 

Formation  of  Urea.  The  liver  is  now  regarded  by  many  physiologists 
to  be  the  principal  organ  concerned  in  urea  formation.  The  liver  normally 
contains  a  certain  amount  of  urea,  and  if  blood  be  passed  through  the 
excised  liver  of  an  animal  which  has  been  in  full  digestion,  a  large  amount 
of  urea  is  obtained.  The  clinical  evidence  proves  that  in  destructive  dis- 
eases of  the  liver  substance  there  is  at  once  a  falling  off  in  urea  elimination. 
Various  drugs  which  increase  liver  action  increase  the  urea  in  the  urine. 

Elaboration  of  Blood.  Besides  the  capability  of  secreting  bile,  the 
liver  possesses  the  property  of  so  acting  upon  and  modifying  the  chemical 
composition  of  the  products  of  digestion,  as  they  traverse  its  substance, 
that  they  readily  assimilate  with  the  blood,  and  are  transformed  into  mate- 
rials capable  of  being  converted  into  the  elements  of  the  blood  and  solid 
tissues. 

The  albuminose  particularly  requires  the  modifying  influence  of  the 
liver ;  for  if  it  be  removed  from  the  portal  vein  and  introduced  into  the 
jugular  vein,  it  is  at  once  removed  from  the  blood  by  the  action  of  the 
kidneys. 

The  blood  of  the  hepatic  vein  differs  from  the  blood  of  the  portal  vein, 
in  being  richer  in  blood  corpuscles,  both  red  and  white ;  its  plasma  is  more 
dense,  containing  a  less  percentage  of  water  and  a  greater  amount  of  solid 
constituents,  but  no  fibrin ;  its  serum  contains  less  albumin,  fats  and  salts, 
but  its  sugar  is  increased. 

Influence  of  the  Nervous  System.  The  nervous  system  directly 
controls  the  functional  activity  of  the  liver,  and  more  especially  its  glyco- 
genic  function.  It  was  discovered  by  Bernard  that  puncture  of  the  medulla 
oblongata  is  followed  by  such  an  enormous  production  of  sugar  that  it  is  at 
once  excreted  by  the  kidneys,  giving  rise  to  diabetic  or  saccharine  urine. 
This  part  of  the  medulla  is,  however,  the  vasomotor  centre  for  the  blood 
vessels  of  the  liver.  Destruction  of  this  centre,  or  injury  to  the  vasomotor 


88  HUMAN   PHYSIOLOGY. 

nerves  emanating  from  it  in  any  part  of  their  course,  is  followed  at  once  by 
dilatation  of  the  hepatic  blood  vessels,  slowing  of  the  blood  current,  a  pro- 
found disturbance  of  the  normal  relation  existing  between  the  blood  and 
liver  cells,  and  a  production  of  sugar.  Many  of  the  hepatic  vasomotor 
nerves  may  be  traced  down  the  cord  as  far  as  the  lumbar  region,  while 
others  leave  the  cord  high  up  in  the  neck  and  enter  the  cervical  ganglia  of 
the  sympathetic  and  so  reach  the  liver.  Injury  to  the  sympathetic  ganglia 
is  often  followed  by  diabetes.  Peripheral  stimulation  of  various  nerves, 
e.  £•.,  sciatic,  pneumogastric,  depressor  nerve,  as  well  as  the  direct  action  of 
many  drugs,  impair  or  depress  the  hepatic  vasomotor  centre  and  so  give 
rise  to  diabetes. 

SKIN. 

The  Skin,  the  external  investment  of  the  body,  is  a  most  complex  and 
important  structure,  serving  (l)  as  a  protective  covering ;  (2)  an  organ  for 
tactile  sensibility ;  (3)  an  organ  for  the  elimination  of  excrementitious 
matters. 

The  Amount  of  Skin  investing  the  body  of  a  man  of  average  size  is 
about  twenty  feet,  and  varies  in  thickness,  in  different  situations,  from  the 
\  to  the  T^  of  an  inch. 

The  skin  consists  of  two  principal  layers,  viz.,  a  deeper  portion,  the 
Corium,  and  a  superficial  portion,  the  Epidermis. 

The  Corium,  or  Cutis  Vera,  may  be  subdivided  into  a  reticulated  and 
a  papillary  layer.  The  former  is  composed  of  white  fibrous  tissue,  non- 
striated  muscular  fibres  and  elastic  tissue,  interwoven  in  every  direction, 
forming  an  areolar  network,  in  the  meshes  of  which  are  deposited  masses 
of  fat,  and  a  structureless  amorphous  matter ;  the  latter  is  formed  mainly  of 
club-shaped  elevations  or  projections  of  the  amorphous  matter,  constituting 
\hz  papilla  ;  they  are  most  abundant,  and  well  developed,  upon  the  palms 
of  the  hands  and  the  soles  of  the  feet;  they  average  the  ^  of  an  inch 
in  length,  and  may  be  simple  or  compound ;  they  are  well  supplied  with 
nerves,  blood  vessels  and  lymphatics. 

The  Epidermis  or  Scarf  Skin  is  an  extra-vascular  structure,  a  product 
of  the  true  skin,  and  composed  of  several  layers  of  cells.  It  may  be 
divided  into  two  layers,  the  rete  mucosum  or  the  Malpighian  layer,  and 
the  horny  or  corneous. 

The  former  closely  applies  itself  to  the  papillary  layer  of  the  true  skin, 
and  is  composed  of  large,  nucleated  cells,  the  lowest  layer  of  which,  the 
"  prickle  cells,"  contain  pigment  granules,  which  give  to  the  skin  its  varying 


APPENDAGES   OF   THE  SKIN.  89 

tints  in  different  individuals  and  in  different  races  of  men  ;  the  more  super- 
ficial cells  are  large,  colorless,  and  semi-transparent.  The  latter,  the  corne- 
ous layer,  is  composed  of  flattened  cells,  which,  from  their  exposure  to  the 
atmosphere,  are  hard  and  horny  in  texture  ;  it  varies  in  thickness  from  y& 
of  an  inch  on  the  palms  of  the  hands  and  feet,  to  the  ^-Q  of  an  inch  in  the 
external  auditory  canal. 


APPENDAGES  OF  THE  SKIN. 

Hairs  are  found  in  almost  all  portions  of  the  body,  and  can  be  divided 
into  (i)  long,  soft  hairs,  on  the  head;  (2)  short,  stiff  hairs,  along  the  edges 
of  the  eyelids  and  nostrils  ;  (3)  soft,  downy  hairs,  on  the  general  cutaneous 
surface.  They  consist  of  a  root  and  a  shaft,  which  is  oval  in  shape,  and 
about  the  ?^  of  an  inch  in  diameter ;  it  consists  of  fibrous  tissue,  covered 
externally  by  a  layer  of  imbricated  cells,  and  internally  by  cells  containing 
granular  and  pigment  material. 

The  Root  of  the  hair  is  embedded  in  the  hair  follicle,  formed  by  a  tubular 
depression  of  the  skin,  extending  nearly  through  to  the  subcutaneous  tissue  ; 
its  walls  are  formed  by  the  layers  of  the  corium,  covered  by  epidermic  cells. 
At  the  bottom  of  the  follicle  is  a  papillary  projection  of  amorphous  matter, 
corresponding  to  a  papillae  of  the  true  skin,  containing  blood  vessels  and 
nerves,  upon  which  the  hair  root  rests.  The  investments  of  the  hair  roots 
are  formed  of  epithelial  cells,  constituting  the  internal  and  external  root 
sheaths. 

The  hair  protects  the  head  from  the  heat  of  the  sun  and  cold,  retains  the 
heat  of  the  body,  prevents  the  entrance  of  foreign  matter  into  the  lungs, 
nose,  ears,  etc.  The  color  is  due  to  the  pigment  matter,  which,  in  old  age, 
becomes  more  or  less  whitened. 

The  Sebaceous  Glands,  imbedded  in  the  true  skin,  are  simple  and 
compound  racemose  glands,  opening,  by  a  common  excretory  duct,  upon 
the  surface  of  the  epidermis  or  into  the  hair  follicle.  They  are  found  in 
all  portions  of  the  body,  most  abundantly  in  the  face,  and  are  formed  by  a 
delicate,  structureless  membrane,  lined  by  flattened  polyhedral  cells.  The 
sebaceous  glands  secrete  a  peculiar  oily  matter,  the  sebum,  by  which  the 
skin  is  lubricated  and  the  hairs  softened ;  it  is  quite  abundant  in  the  region 
of  the  nose  and  forehead,  which  often  present  a  greasy,  glistening  appear- 
ance ;  it  consists  of  water,  mineral  salts,  fatty  globules,  and  epithelial 
cells. 

The  Vernix  caseosa  which  frequently  covers  the  surface  of  the  foetus  at 


90  HUMAN   PHYSIOLOGY. 

birth  consists  of  the  residue  of  the  sebaceous  matters,  containing  epithelial 
cells  and  fatty  matters;  it  seems  to  keep  the  skin  soft  and  supple,  and 
guards  it  from  the  effects  of  the  long-continued  action  of  water. 

The  Sudoriparous  Glands  excrete  the  sweat ;  they  consist  of  a  mass 
or  coil  of  a  tubular  gland  duct,  situated  in  the  derma  and  in  the  subcuta- 
neous tissue ;  average  the  7^  of  an  inch  in  diameter,  and  are  surrounded  by 
a  rich  plexus  of  capillary  blood  vessels.  From  this  coil  the  duct  passes  in  a 
straight  direction  up  through  the  skin  to  the  epidermis,  where  it  makes  a 
few  spiral  turns  and  opens  obliquely  upon  the  surface.  The  sweat  glands 
consist  of  a  delicate  homogeneous  membrane  lined  by  epithelial  cells, 
whose  function  is  to  extract  from  the  blood  the  elements  existing  in  the 
perspiration. 

The  glands  are  very  abundant  all  over  the  cutaneous  surface,  as  many  as 
3528  to  the  square  inch,  according  to  Erasmus  Wilson. 

The  Perspiration  is  an  excrementitious  fluid,  clear,  colorless,  almost 
odorless,  slightly  acid  in  reaction,  with  a  specific  gravity  of  1.003  or  I-OO4- 

The  total  quantity  of  perspiration  excreted  daily  has  been  estimated  at 
about  two  pounds,  though  the  amount  varies  with  the  nature  of  the  food 
and  drink,  exercise,  external  temperature,  season,  etc. 

The  elimination  of  the  sweat  is  not  intermittent,  but  continuous ;  but  it 
takes  place  so  gradually  that  as  fast  as  it  is  formed  it  passes  off  by  evapora- 
tion as  insensible  perspiration.  Under  exposure  to  great  heat  and  exercise 
the  evaporation  is  not  sufficiently  rapid,  and  it  appears  as  sensible  perspira- 
tion. 

COMPOSITION  OF  SWEAT. 

Water, 995-573 

Urea, .  0.043 

Fatty  matters, 0.014 

Alkaline  lactates, 0.317 

Alkaline  sudorates,      1.562 

Inorganic  salts, 2.491 


1000.00 

Urea  is  a  constant  ingredient. 

Carbonic  acid  is  also  exhaled  from  the  skin,  the  amount  being  about  ^ 
of  that  from  the  lungs. 

Perspiration  regulates  the  temperature,  and  removes  waste  matters  from 
the  blood ;  it  is  so  important,  that  if  elimination  be  prevented  death  occurs 
in  a  short  time. 

Influence  of  the  Nervous  System.  The  secretion  of  sweat  is  regu- 
lated by  the  nervous  system.  Here,  as  in  the  secreting  glands,  the  fluid  is 


APPENDAGES  OF  THE  SKIN.  91 

formed  from  material  in  the  lymph  spaces  surrounding  the  gland.  Two 
sets  of  nerves  are  concerned,  viz :  vasomoior,  regulating  the  blood  supply ; 
and  secretory,  stimulating  the  activities  of  the  gland  cells.  Generally  the 
two  conditions,  increased  blood  flow  and  increased  glandular  action,  coexist. 
At  times  profuse  clammy  perspiration  occurs,  with  diminished  blood  flow. 

The  dominating  sweat  centre  is  located  in  the  medulla,  though  subordi- 
nate centres  are  present  in  the  cord.  The  secretory  fibres  reach  the  perspi- 
ratory glands  of  the  head  and  face  through  the  cervical  sympathetic ;  of  the 
arms,  through  the  thoracic  sympathetic,  ulnar  and  radial  nerves ;  of  the  leg, 
through  the  abdominal  sympathetic  and  sciatic  nerves. 

The  sweat  centre  is  excited  to  action  by  mental  emotions,  increased  tem- 
perature of  blood  circulating  in  the  medulla  and  cord,  increased  venosity 
of  blood,  and  many  drugs,  rise  of  external  temperature,  exercise,  etc. 


92  HUMAN   PHYSIOLOGY. 


NERVOUS  SYSTEM. 

The  Nervous  System  coordinates  all  the  various  organs  and  tissues 
of  the  body,  and  brings  the  individual  into  conscious  relationship  with 
external  nature  by  means  of  sensation,  motion,  language,  mental  and  moral 
manifestations. 

The  Nervous  Tissue  may  be  divided  into  two  systems,  the  Cerebro- 
spinal  and  the  Sympathetic. 

(1)  The  Cerebro-spinal  System,  occupies  the  cavities  of  the  cranium 
and  spinal  canal,  and  consists  of  the  brain,  the  spinal  cord,  the  cranial  and 
spinal  nerves.     It  is  the  system  of  animal  life,  and  presides  over  the  func- 
tions of  sensation,  motion,  etc. 

(2)  The  Sympathetic  System,  situated  along  each  side  of  the  spinal 
column,  consists  (i)  of  a  double  chain  of  ganglia,  united  together  by  nerve 
cords,  and  extends  from  the  base  of  the  cranium  to  the  coccyx  ;  (2)  of  various 
ganglia,  situated  in  the  head  and  face,  thorax,  abdomen,  pelvis,  etc.     All 
the  ganglia  are  united  together  by  numerous  communicating  fibres,  many 
of  which  anastomose  with  the.  fibres  of  the  cerebro-spinal  system.     It  is 
the  nervous  system  of  organic  life,  and  governs  the  functions  of  nutrition, 
growth,  etc. 

Nervous  Tissue  is  composed  of  two  kinds  of  matter,  the  gray  and 
white,  which  differ  in  their  color,  structure  and  physiological  endowments  ; 
the  former  consists  of  vesicles  or  cells  which  receive  and  generate  nerve 
force;  the  latter  consists  of  fibres  which  simply  conduct  it,  either  from  the 
periphery  to  the  centre  or  the  reverse. 

Structure  of  Gray  matter.  The  gray  matter  found  on  the  surface  of 
the  brain  in  the  convolutions,  in  the  interior  of  the  spinal  cord,  and  in  the 
various  ganglia  of  the  cerebro-spinal  and  sympathetic  nervous  systems, 
consists  of  a  fine  connective  tissue  stroma,  the  neuroglia,  in  the  meshes  of 
which  are  embedded  the  gray  cells  or  vesicles. 

The  cells  are  grayish  in  color,  and  consist  of  a  delicate  investing  capsule 
containing  a  soft,  granular,  albuminous  matter,  a  nucleus,  and  sometimes  a 
nucleolus.  Some  of  the  cells  are  spherical  or  oval  in  shape,  while  others 
have  an  interrupted  outline,  on  account  of  having  one,  two  or  more  pro- 
cesses issuing  from  them,  constituting  the  tint-polar,  bi-polar  or  multi-polar 
nerve  cells.  Cells  vary  in  size ;  the  smallest  being  found  in  the  brain,  the 


NERVOUS   SYSTEM.  93 

largest  in  the  anterior  horns  of  gray  matter  of  the  spinal  cord.  Some  of 
the  cell  processes  become  continuous  with  the  fibres  of  the  white  matter, 
while  others  anastomose  with  those  of  adjoining  cells  and  form  a  plexus. 

Structure  of  the  White  Matter.  The  white  matter,  found  for  the 
most  part  in  the  interior  of  the  brain,  on  the  surface  of  the  spinal  cord,  and 
in  almost  all  the  nerves  of  the  cerebro-spinal  and  sympathetic  systems, 
consists  of  minute  tubules  or  fibres,  the  ultimate  nerve  filaments,  which  in 
the  perfectly  fresh  condition,  are  apparently  structureless  and  homogeneous ; 
but  when  carefully  examined  after  death  are  seen  to  consist  of  three  distinct 
portions,  (i)  a  tubular 'membrane;  (2)  the  white  substance  of  Schwann ; 
(3)  the  axis  cylinder. 

The  Tubular  membrane,  investing  the  nerve  filament,  is  thin,  homoge- 
neous, and  lined  by  large,  oval  nuclei,  and  presents,  in  its  course,  annular 
constrictions ;  it  serves  to  keep  the  internal  parts  of  the  fibre  in  position, 
and  protects  them  from  injury. 

The  White  substance  of  Schwann,  or  the  medullary  layer,  is  situated 
immediately  within  the  tubular  membrane,  and  gives  to  the  nerves  their 
peculiar  white  and  glistening  appearance.  It  is  composed  of  oleaginous 
matter  in  a  more  or  less  fluid  condition ;  after  death  it  undergoes  coagula- 
tion, giving  to  the  fibre  a  knotted  or  varicose  appearance.  It  serves  to 
insulate  the  axis  cylinder,  and  prevents  the  diffusion  of  the  nerve  force. 

The  Axis  cylinder  occupies  the  centre  of  the  medullary  substance.  In 
the  natural  condition  it  is  transparent  and  invisible,  but  when  treated  with 
proper  reagents,  it  presents  itself  as  a  pale,  granular,  flattened  band,  albu- 
minous in  character,  more  or  less  solid,  and  somewhat  elastic.  It  is  com- 
posed of  a  number  of  minute  fibrillae  united  together  to  form  a  single 
bundle.  (Schultze.) 

Nerve  fibres  in  which  these  three  structural  elements  coexist  are  known 
as  the  medullated  nerve  fibres.  In  the  sympathetic  system,  and  in  the  gray 
substance  of  the  cerebro-spinal  system,  many  nerves  are  destitute  of  a  me- 
dullary layer,  and  are  known  as  the  non-medullated  nerve  fibres. 

Gray  or  Gelatinous  nerve  fibres,  found  principally  in  the  sympathetic 
system,  are  gray  in  color,  semi-transparent,  flattened,  with  distinct  borders, 
finely  granular,  and  present  oval  nuclei. 

The  diameter  of  the  gelatinous  fibres  is  about  the  ^Vff  °^  an  mc^ »  °^ 
the  medullated  fibres  from  ^^  to  T3^  of  an  inch. 

Ganglia  are  small  bodies,  varying  considerably  in  size,  situated  on  the 
posterior  roots  of  spinal  nerves,  on  the  sensory  cranial  nerves,  alongside  of 
the  vertebral  column,  forming  a  connecting  chain,  and  in  the  different 


94  HUMAN   PHYSIOLOGY. 

viscera.  They  consist  of  a -dense,  investing,  fibrous  membrane,  containing 
in  its  interior  gray  or  vesicular  cells,  among  which  are  found  white  and  gela- 
tinous nerve  fibres.  They  may  be  regarded  as  independent  nerve  centres. 

Structure  of  Nerves.  Within  the  cranial  and  spinal  cavities,  the  nerve 
fibres  are  bound  together  by  connective  tissue  in  the  form  of  continuous 
bundles.  Through  the  foramina  of  these  cavities  the  nerve  fibres  emerge 
in  the  form  of  rounded  or  flattened  cords  which  are  termed  nerves.  Each 
nerve  is  surrounded  by  a  sheath  of  connective  tissue,  the  neurilemma, 
which  also  forms  a  stroma  in  which  the  blood  vessels  ramify,  furnishing 
nutritive  material  for  the  growth  and  repair  of  the  ultimate  nerve  fibres. 

A  Nerve  consists  of  a  greater  or  less  number  of  ultimate  nerve  filaments, 
separated  into  bundles  by  fibrous  septa  given  off  from  the  neurilemma.  The 
nerve  filaments  pursue  an  uninterrupted  course,  from  their  origin  to  their 
termination;  branches  pass  from  one  nerve  trunk  into  the  sheath  of 
another,  but  there  is  no  anastomosis  or  coalescence  with  adjoining  nerve 
fibres.  Nerves  are  channels  of  connection  between  the  brain  and  cord, 
and  the  muscles,  glands,  skin,  mucous  membranes,  etc.,  in  which  they  ter- 
minate. Any  excitation  at  either  end  produces  in  the  nerve  an  impulse 
which  travels  throughout  the  length  of  the  fibre.  If  the  nerve  fibres  going 
to  a  muscle  or  gland  are  stimulated,  there  is  increased  muscular  movement, 
and  increased  secretion ;  if  the  nerve  fibres  distributed  to  the  skin  or  mucous 
membranes  are  stimulated,  there  is  produced  in  the  brain  a  sensation.  This 
difference  in  effects  produced  by  irritation  has  led  to  a  division  of  fibres 
into  two  classes:  viz.,  I.  Efferent  or  motor.  2.  Afferent  or  sensory.  There 
is  no  anatomical  or  chemical  difference  discoverable  between  these  two 
classes  of  fibres. 

A  Plexus  is  formed  by  a  number  of  branches  of  different  nerves  inter- 
lacing in  every  direction,  in  the  most  intricate  manner,  but  from  which 
fibres  are  again  given  off  to  pursue  their  independent  course,  e.  g.,  brachial, 
cervical,  lumbar,  sacral,  cardiac  plexuses,  etc. 

Nerve  Terminations,  (i)  Central.  Both  motor  and  sensory  nerve 
fibres,  as  they  enter  the  spinal  cord  and  brain,  lose  their  external  invest- 
ments, and  retaining  only  the  axis  cylinder,  ultimately  become  connected 
with  the  processes  of  the  gray  cells. 

(2)  Peripheral.  As  the  nerves  approach  the  tissues  to  which  they  are 
to  be  distributed,  they  inosculate  freely,  forming  a  plexus  from  which  the 
ultimate  fibres  proceed  to  individual  tissues. 

Motor  Nerves.  In  the  voluntary  or  striped  muscles  the  motor  nerves 
are  connected  with  the  contractile  substance  by  means  of  the  "  motorial 


PROPERTIES  AND  FUNCTIONS  OF  NERVES.  95 

end plates  /"  when  the  nerve  enters  the  muscular  fibre  the  tubular  mem- 
brane blends  with  the  sarcolemma,  the  medullary  layer  disappears,  and  the 
axis  cylinder  spreads  out  into  the  form  of  a  little  plate,  granular  in  charac- 
ter, and  containing  oval  nuclei. 

In  the  unstriped  or  involuntary  muscles,  the  terminal  nerve  fibres  form 
a  plexus  on  the  muscular  fibre  cells,  and  become  connected  with  the  granu- 
lar contents  of  the  nuclei. 

In  the  glands  nerve  fibres  have  been  traced  to  the  glandular  cells,  where 
they  form  a  branching  plexus  from  which  fibres  pass  into  their  interior  and 
become  connected  with  their  substance,  and  thus  influence  secretion. 

Sensitive  Nerves  terminate  in  the  skin  and  mucous  membranes,  in 
three  distinct  modes,  <?.  g.,  as  tactile  corpuscles,  Pacinian  corpuscles,  and  as 
end  bulbs. 

The  tactile  corpuscles  are  found  in  the  papillae  of  the  true  skin,  especially 
on  the  palmar  surface  of  the  hands  and  fingers,  feet  and  toes ;  they  are 
oblong  bodies,  measuring  about  ^ ^  of  an  inch  in  length,  consisting  of  a 
central  bulb  of  homogeneous  connective  tissue  surrounded  by  elastic  fibres 
and  elongated  nuclei.  The  nerve  fibre  approaches  the  base  of  the  corpus- 
cle, makes  two  or  three  spiral  turns  around  it,  and  terminates  in  loops. 
They  are  connected  with  the  sense  of  touch. 

The  Pacinian  corpuscles  are  found  chiefly  in  the  subcutaneous  cellular 
tissue,  on  the  nerves  of  the  hands  and  feet,  the  intercostal  nerves,  the 
cutaneous  nerves,  and  in  many  other  situations.  They  are  oval  in  shape, 
measure  about  the  -fa  of  an  inch  in  length  on  the  average,  and  consist  of 
concentric  layers  of  connective  tissue  ;  the  nerve  fibre  penetrates  the  cor- 
puscle and  terminates  in  a  rounded  knob  in  the  central  bulb.  Their  function 
is  unknown. 

The  end  bulbs  of  Krause  are  formed  of  a  capsule  of  connective  tissue  in 
which  the  nerve  fibre  terminates  in  a  coiled  mass  or  bulbous  extremity ; 
they  exist  in  the  conjunctiva,  tongue,  glans  penis,  clitoris,  etc. 

Many  sensitive  nerves  terminate  in  the  papillae  at  the  base  of  the  hair 
follicle ;  but  in  the  skin,  mucous  membranes,  and  organs  of  special  sense 
their  mode  of  termination  is  not  well  understood. 


PROPERTIES  AND  FUNCTIONS  OF  NERVES. 

Classification.     Nerves  may  be  divided  into  two  groups,  viz.  : — 
( i )  Afferent  or  centripetal,  as  when  they  convey  to  the  nerve  centres  the 
impressions  which  are  made  upon  ^their  peripheral  extremities  or  parts  of 
their  course.     They  may  be  sensitive,  when  they  transmit  impressions  which 


96  HUMAN  PHYSIOLOGY. 

give  rise  to  sensations ;  reflective  or  excitant,  when  the  impression  carried 
to  the  nerve  centre  is  reflected  outward  by  an  efferent  nerve  and  produces 
motion  or  some  other  effect  in  the  part  to  which  the  nerve  is  distributed. 

(2)  Efferent  or  centrifugal,  as  when  the  impulses  generated  in  the  centres 
are  transmitted  outward  to  the  muscles  and  various  organs.  They  may  be 
motor,  as  when  they  convey  impulses  to  the  voluntary  and  involuntary 
muscles;  vasomotor,  when  they  regulate  the  calibre  of  the  small  blood 
vessels,  increasing  or  diminishing  the  amoimt  of  blood  to  a  part ;  secretory, 
when  they  influence  secretion ;  trophic,  when  they  influence  nutrition ; 
inhibitory,  when  they  conduct  impulses  which  produce  a  restraining  or 
inhibiting  action. 

Irritability,  excitability,  neurility.  All  nerves  possess  the  property  of 
being  called  into  action  by  a  stimulus  in  virtue  of  the  possession  of  an 
ultimate  and  inherent  property  denominated  irritability  or  excitability, 
which  is  manifested  so  long  as  the  physical  and  chemical  integrity  of  the 
nerve  is  maintained.  During  the  period  of  excitement,  no  change  in  the 
nerve  is  appreciable  except  an  electrical  one. 

The  irritability  of  a  motor  nerve  is  demonstrated  by  the  contraction  of 
the  muscles  to  which  it  is  distributed;  the  impulse  aroused  by  an  irritant 
travels  outward  to  the  muscles  and  calls  forth  a  contraction. 

The  irritability  of  a  sensory  nerve  is  demonstrated  by  the  development 
of  a  conscious  sensation.  An  irritation  applied  to  a  sensory  nerve  in  any 
part  of  its  course  arouses  an  impulse  which  travels  to  the  brain  and  produces 
there  a  sensation.  The  irritability  of  a  sensory  nerve  may  be  increased  by 
congestion  or  inflammation  and  decreased  by  cold,  compression  and  injuries. 
Other  tissues — e.g.,  muscles,  glands,  etc. — possess  irritability,  and  when 
subjected  to  the  action  of  a  stimulus  react  in  their  own  particular  way.  The 
irritability  of  nerves  is  distinct  and  independent  of  the  irritability  of  muscles 
and  glands,  as  can  be  demonstrated  by  the  use  of  poisons,  such  as  woorara, 
atropia,  etc. 

The  properties  of  sensation  and  motion  reside  in  different  nerve  fibres. 
Motor  nerves  can  be  destroyed  or  paralyzed  by  the  introduction  of 
woorara  under  the  skin,  without  affecting  sensation  ;  the  sensibility  of 
nerves  can  be  abolished  by  the  employment  of  anaesthetics  without  destroy- 
ing motion. 

In  the  transmission  of  the  nerve  impulse  the  axis  cylinder  is  the  essential 
conducting  agent,  the  white  substance  of  Schwann  and  tubular  membrane 
being  probably  accessory  structures,  protecting  the  axis  from  injury,  and 
preventing  the  diffusion  of  nerve  force  to  adjoining  nerves. 

Nerve  Degeneration.     When  nerves  are  separated  from  their   trophic 


PROPERTIES   AND    FUNCTIONS   OF   NERVES.  97 

or  nutritive  centres,  they  degenerate  progressively  in  the  direction  in 
which  they  conduct  impressions.  In  motor  nerves,  from  the  centre  to  the 
periphery;  in  sensory  nerves,  from  the  periphery  to  the  centres. 

Stimuli  of  Nerves.  Nerves  do  not  possess  the  power  of  spontaneously 
generating  and  propagating  nerve  impulses ;  they  can  only  be  aroused  to 
activity  by  the  action  of  an  extra-neural  stimulus.  In  the  living  condition, 
the  stimuli  capable  of  throwing  the  nerve  into  an  active  condition  act  for 
the  most  part  on  either  the  central  or  peripheral  end  of  the  nerve.  In  the 
case  of  motor  nerves  the  stimulus  to  the  excitation,  originating  in  some 
molecular  disturbance  in  the  nerve  cells,  acts  upon  the  nerve  fibres  in  con- 
nection with  them.  In  the  case  of  sensory  or  afferent  nerves  the  stimuli  act 
upon  the  peculiar  end  organs  with  which  the  sensory  nerves  are  in  connec- 
tion, which  in  turn  excite  the  nerve  fibres.  Experimentally,  it  can  be 
demonstrated  that  nerves  can  be  excited  by  a  sufficiently  powerful  stimulus 
applied  in  any  part  of  their  extent. 

Nerves  respond  to  stimulation  according  to  their  habitual  function;  thus, 
stimulation  of  a  sensory  nerve,  if  sufficiently  strong,  results  in  the  sensation 
of  pain;  of  the  optic  nerve,  in  the  sensation  of  light;  of  a  motor  nerve,  in 
contraction  of  the  muscle  to  which  it  is  distributed ;  of  a  secretory  nerve, 
in  the  activity  of  the  related  gland,  etc.  It  is,  therefore,  evident  that  pecu- 
liarity of  nervous  function  depends  neither  upon  any  special  construction  or 
activity  of  the  nerve  itself,  nor  upon  the  nature  of  the  stimulus,  but  entirely 
upon  the  peculiarities  of  its  central  and  peripheral  end  organs. 

Nerve  stimuli  may  be  divided  into :  1st,  General  stimuli,  comprising 
those  agents  which  are  capable  of  exciting  a  nerve  in  any  part  of  its  course ; 
2d,  Special  stimuli,  comprising  those  agents  which  act  upon  nerves  only 
through  the  intermediation  of  the  end  organs. 

General  stimuli  : — 

1.  Mechanical :  as  from  a  blow,  pressure,  tension,  puncture,  etc. 

2.  Thermal:  heating  a  nerve  at  first  increases  and  then  decreases  its 

excitability. 

3.  Chemical :  Sensory  nerves  respond  somewhat  less  promptly  than  motor 

nerves  to  this  form  of  irritation. 

4.  Electrical ;  Either  the  constant  or  interrupted  current. 

5.  The  normal  physiological  stimulus: — 

(a)  Centrifugal  or  afferent  if  proceeding  from  the  centre  toward  the 

periphery. 
(l>)  Centripetal  or  afferent  if  in  the  reverse  direction. 


98  HUMAN   PHYSIOLOGY. 

Special  stimuli  : — 

1.  Light  or  ethereal  vibrations  acting  upon  the  end  organs  of  the  optic 

nerve  in  the  retina. 

2.  Sound  or  atmospheric  undulations  acting  upon  the  end  organs  of  the 

auditory  nerve. 

3.  Heat  or  vibrations  of  the  air  acting  upon  the  end  organs  in  the  skin. 

4.  Chemical  agencies  acting  upon  the  end  organs  of  the  olfactory  and 

gustatory  nerves. 

As  to  the  nature  of  the  nerve  impulse  generated  by  the  above  stimuli  but 
little  is  known.  It  is  supposed  to  be  a  mode  of  motion,  molecular  or 
vibratory  in  character,  which  passes  through  the  axis  cylinder  with  a  definite 
velocity. 

Rapidity  of  Transmission  of  Nerve  Force.  The  passage  of  a  nervous 
impulse,  either  from  the  brain  to  the  periphery  or  in  the  reverse  direction, 
requires  an  appreciable  period  of  time.  The  velocity  with  which  the 
impulse  travels  in  human  sensory  nerves  has  been  estimated  at  about  190 
feet  per  second,  and  for  motor  nerves  at  from  100  to  200  feet  per  second. 
The  rate  of  movement  is,  however,  somewhat  modified  by  temperature,  cold 
lessening  and  heat  increasing  the  rapidity ;  it  is  also  modified  by  electrical 
conditions,  by  the  action  of  drugs,  the  strength  of  the  stimulus,  etc.  The 
rate  of  transmission  through  the  spinal  cord  is  considerably  slower  than  in 
nerves,  the  average  velocity  for  voluntary  motor  impulses  being  only  33 
feet  per  second,  for  sensitive  impressions  40  feet,  and  for  tactile  impressions 
146  feet  per  second. 

Phenomena  of  Muscles  and  Nerves.  The  muscles  are  the  motor 
organs  of  the  body  and  constitute  a  large  per  cent,  of  the  body  weight. 
Muscles  are  of  two  kinds,  striated  and  non-striated  or  involuntary.  The 
striated  muscles  consist  of  bundles  of  fibres,  the  fasciculi,  held  together  by 
connective  tissue.  Each  muscle  fibre  is  about  %  to  I  ^  inches  long,  and 
possesses  a  delicate  homogeneous  membrane,  the  sarcolemma,  in  the  interior 
of  which  is  contained  the  contractile  substance,  which  presents  a  striated 
appearance.  During  life  this  substance  is  in  a  fluid  condition,  but  after 
death  undergoes  stiffening. 

The  non-striated  muscles  form  membranes  which  surround  cavities,  e.g., 
stomach,  arteries,  bladder,  etc.  They  are  composed  of  elongated  cells 
without  striations,  and  contain  in  their  interior  one  or  more  nuclei. 

Muscular  tissue  is  composed  of  water,  an  organic  contractile  substance, 
myosin,  non-nitrogenized  substances,  such  as  glycogen,  inosite,  fat,  and 


PROPERTIES   AND   FUNCTIONS  OF   NERVES.  99 

inorganic  salts.  When  at  rest  the  muscle  is  alkaline  in  reaction,  but  during 
and  after  contraction  it  becomes  acfd. 

Muscles  possess  the  properties  of  (i)  Contractility,  which  is  the  capa- 
bility of  shortening  themselves  in  the  direction  of  their  long  axis,  and  at 
the  same  time  becoming  thicker  and  more  rigid.  (2)  Extensibility,  by 
means  of  which  they  are  lengthened  in  proportion  to  weights  attached. 
(3)  Elasticity,  in  virtue  of  which  they  return  to  their  .original  shape  when 
the  force  applied  is  removed. 

The  contractility  of  muscles  is  called  forth  mainly  by  nervous  impulses, 
descending  motor  nerves,  which  originate  in  the  central  nervous  system ; 
but  it  can  also  be  excited  by  the  electric  current,  the  application  of  strong 
acids,  heat,  or  by  mechanical  means. 

Phenomena  of  a  Muscular  Contraction.  When  a  single  induction 
shock  is  propagated  through  a  nerve,  the  muscle  to  which  it  is  distributed 
undergoes  a  quick  pulsation,  and  speedily  returns  to  its  former  condition. 
As  is  shown  by  the  muscle  curve,  the  contraction,  which  is  at  first  slow, 
increases  in  rapidity  to  its  maximum,  gradually  relaxes  and  is  again  at  rest, 
the  entire  pulsation  not  occupying  more  than  the  ^  of  a  second. 

The  muscular  contraction  does  not  instantly  follow  the  induction  shock, 
even  when  the  electrodes  are  placed  directly  upon  the  muscular  fibres 
themselves;  an  appreciable  -period  intervenes  before  the  contraction,  during 
which  certain  chemical  changes  are  taking  place  preparatory  to  the  mani- 
festation" of  force.  This  is  the  "  latent  period,"  which  has  an  average  dura- 
tion of  the  T^ff  of  a  second,  but  varies  with  the  temperature,  the  strength 
of  the  stimulus,  the  animal,  etc.  The  muscular  movements  of  the  body, 
however,  are  occasioned  by  contractions  of  a  much  longer  duration,  depend- 
ing upon  the  number  (the  average,  20)  of  nervous  impulses  passing  to  the 
muscles  in  a  second. 

During  the  muscular  contraction  the  following  phenomena  are  observed, 
viz. :  a  change  in  form,  a  rise  in  temperature,  a  consumption  of  oxygen  and 
an  evolution  of  carbonic  acid ;  the  production  of  a  distinct  musical  sound, 
a  change  from  an  alkaline  to  an  acid  reaction,  from  the  development  of 
sarcolactic  acid;  a  disappearance  of  the  natural  muscle  currents,  which 
under  a  negative  "variation  in  the  "latent  period,"  just  after  the  nervous 
impulse  reaches  the  termination  of  the  nerve,  and  before  the  appearance 
of  the  muscular  contraction  wave. 

Electrical  Currents  in  Muscles  and  Nerves.  If  a  muscle  or  nerve 
be  divided  and  non-polarizable  electrodes  be  placed  upon  the  natural 
longitudinal  surface  at  the  equator,  and  upon  the  transverse  section,  electri- 


100  HUMAN   PHYSIOLOGY. 

cal  currents  are  observed  with  the  aid  of  a  delicate  galvanometer.  The 
direction  of  the  current  is  always  from  the  positive  equatorial  surface  to  the 
negative  transverse  surface.  The  strength  of  the  current  increases  or  dimin- 
ishes according  as  the  positive  electrode  is  moved  toward  or  from  the 
equator.  When  the  electrodes  are  placed  on  the  two  transverse  ends  of  a 
nerve,  an  axial  current  will  be  observed  whose  direction  is  opposite  to  that 
of  the  normal  impulse  in  the  nerve. 

The  electromotive  force  of  the  strongest  nerve  current  has  been  estimated 
to  be  equal  to  the  0.026  of  a  Daniell  battery ;  the  force  of  the  current  of  the 
frog  muscle  about  0.05  to  0.08  of  a  Daniell. 

Negative  Variation  of  Currents  in  Muscles  and  Nerves.  If  a 
muscle  or  nerve  be  thrown  into  a  condition  of  tetanus,  it  will  be  observed  that 
the  currents  undergo  a  diminution  or  negative  variation,  a  change  which 
passes  along  the  nerve  in  the  form  of  a  wave  and  with  a  velocity  equal  to 
the  rate  of  transmission  of  the  nerve  impulse.  The  wave  length  of  a  single 
negative  variation  has  been  estimated  to  be  18  millimetres;  the  period  of 
its  duration  being  from  0.0005  to  0.0008  of  a  second. 

It  is  asserted  by  Hermann  that  perfectly  fresh,  uninjured  muscles  and 
nerves  are  devoid  of  currents,  and  that  the  currents  observed  are  the  result 
of  a  molecular  death  at  the  point  of  section,  this  point  becoming  negative 
to  the  equatorial  point.  He  applies  the  term  "  action  currents  "  to  the  cur- 
rents obtained  when  a  muscle  is  thrown  into  a  state  of  activity. 

Electrical  Properties  of  Nerves.  When  a  galvanic  current  is  made 
to  flow  along  a  motor  nerve  from  the  centre  to  the  periphery,  from  the 
positive  to  the  negative  pole,  it  is  known  as  the  direct,  descending  or  centri- 
fugal current.  When  it  is  made  to  flow  in  the  reverse  direction  it  is  known 
as  the  inverse,  ascending  or  centripetal  current. 

The  passage  of  a  direct  current  enfeebles  the  excitability  of  a  nerve;  the 
passage  of  the  inverse  current  increases  it.  The  excitability  of  a  nerve  may 
be  exhausted  by  the  repeated  applications  of  electricity ;  when  thus 
exhausted  it  may  be  restored  by  repose,  or  by  the  passage  of  the  inverse 
current  if  the  nerve  has  been  exhausted  by  the  direct  current  or  vice  versa. 

During  the  actual  passage  of  a  feeble  constant  current  in  either  direction 
neither  pain  nor  muscular  contraction  is  ordinarily  manifested  ;  if  the  current 
be  very  intense  the  nerve  may  be  disorganized  and  its  excitability  destroyed. 

Electrotonus.  The  passage  of  a  direct  galvanic  current  through  a  por- 
tion of  a  nerve  excites  in  the  parts  beyond  the  electrodes  a  condition  of 
electric  tension  or  electrotonus,  during  which  the  excitability  of  the  nerve 
is  decreased  near  the  anode  or  positive  pole,  and  increased  near  the  kathode 


PROPERTIES  AND   FUNCTIONS   OF   NERVES.  101 

or  negative  pole;  the  increase  of  excitability  in  the  katelectrotonic  area, 
that  nearest  the  muscle,  being  manifested  by  a  more  marked  contraction  of 
the  muscle  than  the  normal,  when  the  nerve  is  irritated  in  this  region.  The 
passage  of  an  inverse  galvanic  current  excites  the  same  condition  of 
electrotonus;  and  the  diminution  of  excitability  near  the  anode,  the  anelec- 
trotonic  area,  that  now  nearest  the  muscle,  being  manifested  by  a  less 
marked  contraction  than  the  normal  when  the  nerve  is  stimulated  in  this 
region.  Between  the  electrodes  is  a  neutral  point  where  the  katelectrotonic 
area  emerges  into  the  anelectrotonic  area.  If  the  current  be  a  strong  one, 
the  neutral  point  approaches  the  kathode;  if  weak,  it  approaches  the 
anode. 

When  a  nervous  impulse  passes  along  a  nerve,  the  only  appreciable  effect 
is  a  change  in  its  electrical  condition,  there  being  no  change  in  its  tempera- 
ture, chemical  composition  or  physical  condition.  The  natural  nerve  cur- 
rents, which  are  always  present  in  a  living  nerve  as  a  result  of  its  nutritive 
activity,  in  great  part  disappear  during  the  passage  of  an  impulse,  under- 
going a  negative  variation. 

Law  of  Contraction.  If  a  feeble  galvanic  current  be  applied  to  a  recent 
and  excitable  nerve,  contraction  is  produced  in  the  muscles  only  upon  the 
making  of  the  circuit  with  both  the  direct  and  inverse  currents. 

If  the  current  be  moderate  in  intensity,  the  contraction  is  produced  in  the 
muscle  both  upon  the  making  and  breaking  of  the  circuit,  with  both  the 
direct  and  inverse  currents. 

If  the  current  be  intense,  contraction  is  produced  only  when  the  circuit 
is  made  with  the  direct  current,  and  only  when  it  is  broken  with  the  inverse 
current. 

The  Reaction  of  Degeneration.  Two  different  applications  of  elec- 
tricity are  used  in  electro-physiology  and  electro-therapeutics — the  constant 
or  galvanic,  and  the  interrupted  or  faradic  currents.  Injured  and  paralyzed 
muscles  and  nerves  react  differently  to  these  two  kinds  of  stimuli,  and  the 
facts  are  of  the  greatest  importance  in  the  diagnosis  and  therapeutics  of  the 
precedent  lesions.  The  principal  difference  of  behavior  relates  to  the 
reaction  of  degeneration — a  condition  produced  by  paralysis  of  any  kind. 
It  is  characterized  by  a  diminished  or  abolished  excitability  of  the  muscles 
to  the  faradic  current,  while  there  is  at  the  same  time  an  increased  excita- 
bility to  the  galvanic  current.  The  synchronous  diminished  excitability  of 
the  nerves  is  the  same  for  either  current.  The  term  partial  reaction  of 
degeneration  is  used  when  there  is  a  normal  reaction  of  the  nerves,  but  the 
muscles  show  the  degenerative  reaction.  This  condition  is  a  characteristic 
of  progressive  muscular  atrophy. 


102  HUMAN   PHYSIOLOGY. 

CRANIAL  NERVES. 

The  Cranial  Nerves  come  off  from  the  base  of  the  brain,  pass  through 
the  foramina  in  the  walls  of  the  cranium,  and  are  distributed  to  the  skin, 
muscles  and  organs  of  sense  in  the  face  and  head. 

According  to  the  classification  of  Soemmering,  there  are  12  pairs  of 
nerves,  enumerating  them  from  before  backward,  as  follows,  viz  : — 

1st  Pair,  or  Olfactory.  7th  Pair,  or  Facial,  Portio  dura. 

2d  Pair,  or  Optic  8th  Pair,  or  Auditory,  Portio  mollis. 

3d  Pair,  or  Motor  oculi  communis.  Qth  Pair,  or  Glosso-pharyngeal. 

4th  Pair,  or  Patheticus,  Trochlearis.  loth  Pair,  or  Pneumogastric. 

5th  Pair,  or  Trifacial,  Trigeminus.  I  ith  Pair,  or  Spinal  accessory. 

6th  Pair,  or  Abducens.  1 2th  Pair,  or  Hypoglossal. 

The  Cranial  Nerves  may  also  be  classified  physiologically,  according 
to  their  function,  into  three  groups  :  I.  Nerves  of  special  sense.  2.  Nerves 
of  motion.  3.  Nerves  of  general  sensibility. 

ist  Pair.     Olfactory. 

Apparent  Origin.  From  the  inferior  and  internal  portion  of  the  ante- 
rior lobes  of  the  cerebrum  by  three  roots,  viz :  an  external  white  root,  which 
passes  across  the  fissure  of  Sylvius  to  the  middle  lobe  of  the  cerebrum ;  an 
internal  white  root,  from  the  most  posterior  part  of  the  anterior  lobe ;  &gray 
root,  from  the  gray  matter  in  the  posterior  and  inner  portion  of  the  inferior 
surface  of  the  anterior  lobe. 

Deep  Origin.     Not  satisfactorily  determined. 

Distribution.  The  olfactory  nerve,  formed  by  the  union  of  the  three 
roots,  passes  forward  along  the  under  surface  of  the  anterior  lobe  to  the 
ethmoid  bone,  where  it  expands  into  the  olfactory  bulb.  This  bulb  con- 
tains ganglionic  cells,  is  grayish  in  color  and  soft  in  consistence ;  it  gives  off 
from  its  under  surface  from  fifteen  to  twenty  nerve  filaments,  the  true 
olfactory  nerves,  which  pass  through  the  cribriform  plate  of  the  ethmoid 
bone,  and  are  distributed  to  the  schneiderian  mucous  membrane.  This 
membrane  extends  from  the  cribriform  plate  of  the  ethmoid  bone  downward, 
about  one  inch. 

Properties.  The  olfactory  nerves  give  rise  to  neither  motor  nor  sensory 
phenomena  when  stimulated.  They  carry  simply  the  special  impressions 
of  odorous  substances.  Destruction  or  injury  of  the  olfactory  bulbs  is 
attended  by  a  loss  of  the  sense  of  smell. 

Function.  Governs  the  sense  of  smell.  Conducts  the  impressions  which 
give  rise  to  odorous  sensations. 


CRANIAL   NERVES.  103 

2d  Pair.     Optic. 

Apparent  Origin.     From  the  anterior  portion  of  the  optic  commissure. 

Deep  Origin.  The  origins  and  connections  of  the  optic  tract  are  very 
complex.  The  immediate  origins  are  bands  of  fibres  from  the  thalamus 
opticus  and  anterior  corpora  quadrigemina.  The  corpora  geniculata  are 
interposed  ganglia.  The  ultimate  roots  are  traced — 

1.  By  a  broad  band  of  fibres — "  the  optic  radiation  of  Gratiolet  " — to  the 

psycho-optic  centres  in  the  occipital  lobes. 

2.  To  the  gyrus  hippocampi  and  sphenoidal  lobes. 

3.  Through  the  corpus  callosum  to  the  motor  areas  of  the  opposite  cere- 

bral hemispheres. 

4.  To  the  frontal  region  by  "  Meynert's  Commissure." 

5.  To  the  spinal  cord. 

6.  To  the  corpora  geniculata,  pulvinar,  and  anterior  corpora  geniculata  by 

ganglionic  roots. 

Distribution.  The  two  roots  unite  to  form  a  flattened  band,  the  optic 
tract,  which  winds  around  the  crus  cerebri  to  decussate  with  the  nerve  of 
the  opposite  side,  forming  the  optic  chiasm.  The  decussation  of  fibres  is 
not  complete ;  some  of  the  fibres  of  the  left  optic  tract  going  to  the  outer 
half  of  the  eye  of  the  same  side,  and  to  the  inner  half  of  the  eye  of  the 
opposite  side ;  the  same  holds  true  for  the  right  optic  tract. 

The  optic  nerves  proper  arise  from  the  commissure,  pass  forward  through 
the  optic  foramina,  and  are  finally  distributed  in  the  retina, 

Properties.  They  are  insensible  to  ordinary  impressions,  and  convey 
only  the  special  impressions  of  light.  Division  of  one  of  the  nerves  is 
attended  by  complete  blindness  in  the  eye  of  the  corresponding  side. 

Hemiopia  and  Hemianopsia.  Owing  to  the  decussation  of  the  fibres 
in  the  optic  chiasm  division  of  the  optic  tract  produces  loss  of  sight  in 
the  outer  half  of  the  eye  of  the  same  side,  and  in  the  inner  half  of  the 
eye  of  the  opposite  side,  the  blind  part  being  separated  from  the  normal  part 
by  a  vertical  line.  The  term  hemiopia  is  applied  to  the  loss  of  function  or 
paralysis  of  the  one-half  of  the  retina;  hemianopsia  is  applied  to  the  blind- 
ness in  the  field  of  vision.  If,  for  example,  the  right  optic  tract  be  divided, 
there  will  be  hemiopia  in  the  outer  half  of  the  right  eye  and  inner  half  of 
left  eye,  thus  causing  left  lateral  hemianopsia,  and  as  the  two  halves  are 
affected  which  correspond  in  normal  vision,  it  is  spoken  of  as  homonymous 
hemianopsia.  Lesion  of  the  anterior  part  of  the  optic  chiasm  causes  blind- 
ness in  the  inner  half  of  the  two  eyes. 


104  HUMAN   PHYSIOLOGY. 

Functions.  Governs  the  sense  of  sight.  Receives  and  conveys  to  the 
brain  the  luminous  impressions  which  give  rise  to  the  sensation  of  sight. 

The  reflex  movements  of  the  iris  are  called  forth  by  the  optic  nerve. 
When  an  excess  of  light  falls  upon  the  retina  the  impression  is  carried 
back  to  the  tubercula  quadrigemina,  where  it  is  transformed  into  a  motor 
impulse,  which  then  passes  outward  through  the  motor  oculi  nerve  to  the 
contractile  fibres  of  the  iris  and  diminishes  the  size  of  the  pupil.  The 
absence  of  light  is  followed  by  a  dilatation  of  the  pupil. 

3d  Pair.     Motor  Oculi  Communis. 
Apparent  Origin.     From  the  inner  surface  of  the  crura  cerebri. 

Deep  Origin.  By  three  sets  of  filaments  coming  from  the  oculo-motorius 
nucleus,  which  lies  under  the  aqueduct  of  Sylvius;  these  three  groups  of 
filaments  are  destined  for  the  innervation  of  the  muscles  of  the  eyeball,  the 
sphincter  pupilbe,  and  the  ciliary  muscle.  By  filaments  coining  from  the 
lenticular  nucleus,  corpora  quadrigemina,  optic  thalamus  ;  these  filaments 
converge  to  form  a  main  trunk,  which  winds  around  the  crus  cerebri,  in 
front  of  the  pons  Varolii. 

Distribution.  The  nerve  then  passes  forward,  and  enters  the  orbit 
through  the  sphenoidal  fissure,  where  it  divides  into  a  superior  branch 
distributed  to  the  superior  rectus  and  levator  palpebra  muscles ;  an  inferior 
branch  sending  branches  to  the  internal  and  inferior  recti,  and  the  inferior 
oblique  muscles ;  filaments  also  pass  into  the  ciliary  or  ophthalmic  ganglion ; 
from  this  ganglion  the  ciliary  nerves  arise  which  enter  the  eyeball,  and  are 
distributed  to  the  circular  fibres  of  the  iris  and  the  ciliary  muscle.  The 
3d  nerve  also  receives  filaments  from  the  cavernous  plexus  of  the  sympa- 
thetic and  from  the  fifth  nerve. 

Properties.  Irritation  of  the  root  of  the  nerve  produces  contraction 
of  the  pupil,  internal  strabismus,  muscular  movements  of  eye,  but  no  pain. 
Division  of  the  nerve  is  followed  by  ptosis  (falling  of  the  upper  eyelid), 
external  strabismus,  due  to  the  unopposed  action  of  the  external  rectus 
muscle ;  paralysis  of  the  accommodation  of  the  eye ;  dilatation  of  the 
pupil  from  paralysis  of  the  circular  fibres  of  the  iris  and  ciliary  muscle; 
and  inability  to  rotate  the  eye,  slight  protrusion  and  double  vision.  The 
images  are  crossed ;  that  of  the  paralyzed  eye  is  a  little  above  that  of  the 
sound,  and  its  upper  end  inclined  toward  it. 

Function.  Governs  movements  of  the  eyeball  by  animating  all  the 
muscles  except  the  external  rectus  and  superior  oblique,  the  movements  of 


CRANIAL  NERVES.  105 

the  iris,  elevates  the  upper  lid,  influences  the  accommodation  of  the  eye 
for  distances.  Can  be  called  into  action  by  (i)  voluntary  stimuli,  (2)  by 
reflex  action  through  irritation  of  the  optic  nerve. 

4th  Pair.     Patheticus. 

Apparent  Origin.     From  the  superior  peduncles  of  the  cerebellum. 

Deep  Origin.  By  fibres  terminating  in  the  corpora  quadrigemina, 
lenticular  nucleus,  valve  of  Vieussens,  and  in  the  substance  of  the  cere- 
bellar  peduncles;  some  filaments  pass  over  the  median  line  and  decussate 
with  fibres  of  the  opposite  side. 

Distribution.  The  nerve  enters  the  orbital  cavity  through  the  sphe- 
noidal  fissure,  and  is  distributed  to  the  superior  oblique  muscle;  in  its 
course  receives  filaments  from  the  ophthalmic  branch  of  the  5th  pair  and  the 
sympathetic. 

Properties.  When  the  nerve  is  irritated  muscular  movements  are  pro- 
duced in  the  superior  oblique  muscle,  and  the  pupil  of  the  eye  is  turned 
downward  and  outward.  Division  or  paralysis  lessens  the  movements 
and  rotation  of  the  globe  downward  and  outward.  The  diplopia  conse- 
quent upon  this  paralysis  is  homonymous,  one  image  appearing  above  the 
other.  The  image  of  the  paralyzed  eye  is  below,  its  upper  end  inclined 
toward  that  of  the  sound  eye. 

Function.  Governs  the  movements  of  the  eyeball  produced  by  the 
action  of  the  superior  oblique  muscles. 

6th  Pair.*     Abducens.     Motor  Oculi  Externus. 

Apparent  Origin.  From  the  groove  between  the  anterior  pyramidal 
body  and  the  pons  Varolii,  where  it  arises  by  two  roots. 

Deep  Origin.     From  the  gray  matter  of  the  medulla  oblongata. 

Distribution.  The  nerve  then  passes  into  the  orbit  through  the  sphe- 
noidal  fissure,  and  is  distributed  to  the  external  rectus  muscle.  Receives 
filaments  from  the  cervical  portion  of  the  sympathetic,  through  the  carotid 
plexus  and  spheno-palatine  ganglion. 

Properties.  When  irritated,  the  external  rectus  muscle  is  thrown  into 
convulsive  movements,  and  the  eyeball  is  turned  outward.  When  divided 

*  The  6th  nerve  is  considered  in  connection  with  the  3d  and  4th  nerves,  since  they 
together  constitute  the  motor  apparatus  by  which  the  ocular  muscles  are  excited  to 
action. 

H 


106  HUMAN   PHYSIOLOGY. 

or  paralyzed,  this  muscle  is  paralyzed ;  motion  of  the  eyeball  outward  past 
the  median  line  is  impossible,  and  the  homonymous  diplopia  increases  as 
the  object  is  moved  outward  past  this  line.  The  images  are  upon  the  same 
plane  and  parallel.  Internal  strabismus  results  because  of  the  unopposed 
action  of  the  internal  rectus. 

Function.     To  turn  the  eyeball  outward. 

5th  Pair.     Trifacial.     Trigeminal. 

Apparent  Origin.     By  two  roots  from  the  side  of  the  pons  Varolli. 

Deep  Origin.  The  deep  origin  of  the  two  roots  is  the  upper  part  of 
the  floor  and  anterior  wall  of  the  4th  ventricle,  by  three  bundles  of  fila- 
ments, one  of  which  anastomoses  with  the  auditory  nerve ;  another  passes 
to  the  lateral  tract  of  the  medulla;  while  a  third,  grayish  in  color,  goes  to 
the  restiform  bodies,  and  may  be  traced  to  the  point  of  the  calamus  scrip- 
torius. 

Filaments  of  origin  have  been  traced  to  the  "  trigeminal  sensory  nucleus," 
located  on  a  level  with  the  point  of  exit  of  the  nerve,  and  to  the  posterior 
gray  horns  of  the  cord,  as  low  down  as  the  middle  of  the  neck. 

Distribution.  The  large  root  of  the  nerve  passes  obliquely  upward 
and  forward  to  the  ganglion  of  Gasser,  which  receives  filaments  of  com- 
munication from  the  carotid  plexus  of  the  sympathetic.  It  then  divides  into 
three  branches. 

1.  Ophthalmic  branch,  which  receives  communicating  filaments  from 
the  sympathetic,  and  sends  sensitive  fibres  to  all  the  motor  nerves  of  the 
eyeball.     It  is  distributed  to  the  ciliary  ganglion,  lachrymal  gland,  sac  and 
caruncle,  conjunctiva,  integument  of  the  upper  eyelid,  forehead,  side  of 
head  and  nose,  anterior  portion  of  the  scalp,  ciliary  muscle  and  iris. 

2.  Superior  maxillary  branch,  sends  branches   to  the  spheno-palatine 
ganglion,  integument  of  the  temple  and  lower  eyelid,  side  of  forehead, 
nose,  cheek  and  upper  lip,  teeth  of  the  upper  jaw,  and  alveolar  processes. 

3.  Inferior  maxillary  branch,  which,  after  receiving  in  its  course  fila- 
ments from  the  small  root  and  from  the  facial,  is  distributed  to  the  sub- 
maxillary  ganglion,  the  parotid  and  sub-lingual  glands,  external  auditory 
meatus,  mucous  membrane  of  the  mouth,  anterior  two-thirds  of  the  tongue 
(lingual  branch),  gums,  arches  of   the  palate,  teeth    of   the    lower  jaw, 
and  integument  of  the  lower   part  of  the    face,  and   to    the   muscles  of 
mastication. 

The  small  root  passes  forward  beneath  the  ganglion  of  Gasser,  through 
the  foramen  ovale,  and  joins  the  inferior  maxillary  division  of  the  large 


CRANIAL   NERVES.  107 

root,  which  then  divides  into  an  anterior  and  posterior  branch,  the  former 
of  which  is  distributed  to  the  muscles  of  mastication,  viz. :  temporal,  mas- 
seter,  internal  and  external  pterygoid  muscles. 

Properties.  It  is  the  most  acutely  sensitive  nerve  in  the  body,  and 
endows  all  the  parts  to  which  it  is  distributed  with  general  sensibility. 

Irritation  of  the  large  root,  or  any  of  its  branches,  will  give  rise  to 
marked  evidence  of  pain ;  the  various  forms  of  neuralgia  of  the  head  and 
face  being  occasioned  by  compression,  disease,  or  exposure  of  some  of  its 
terminal  branches. 

Division  of  the  large  root  within  the  cranium  is  followed  at  once  by  a 
complete  abolition  of  all  sensibility  in  the  head  and  face,  but  is  not  attended 
by  any  loss  of  motion.  The  integument,  mucous  membranes  and  .the  eye 
may  be  lacerated,  cut  or  bruised,  without  the  animal  exhibiting  any  evidence 
of  pain.  At  the  same  time  the  lachrymal  secretion  is  diminished,  the  pupil 
becomes  contracted,  the  eyeball  is  protruded,  and  the  sensibility  of  the 
tongue  is  abolished. 

The  reflex  movements  of  deglutition  are  also  somewhat  impaired ;  the 
impression  of  the  food  being  unable  to  reach  and  excite  the  nerve  centre  in 
the  medulla  oblongata. 

Galvanization  of  the  small  root  produces  movements  of  the  muscles  of 
mastication ;  section  of  the  root  causes  paralysis  of  these  muscles,  and  the 
jaw  is  drawn  to  the  opposite  side,  by  the  action  of  the  opposing  muscles. 

Influence  upon  the  Special  Senses.  After  division  of  the  large  root 
within  the  cranium,  a  disturbance  in  the  nutrition  of  the  special  senses 
sooner  or  later  manifests  itself. 

Sight.  In  the  course  of  twenty-four  hours  the  eye  becomes  very  vascular 
and  inflamed,  the  cornea  becomes  opaque  and  ulcerates,  the  humors  are 
discharged,  and  the  eye  is  totally  destroyed. 

Smell,  The  nasal  mucous  membrane  swells  up,  becomes  fungous,  and 
is  liable  to  bleed  on  the  slightest  irritation.  The  mucus  is  increased  in 
amount,  so  as  to  obstruct  the  nasal  passages  ;  the  sense  of  smell  is  finally 
abolished. 

Hearing.  At  times  the  hearing  is  impaired,  from  disorders  of  nutrition 
in  the  middle  ear  and  external  auditory  meatus. 

Alteration  in  the  nutrition  of  the  special  senses  is  not  marked  if  the  sec- 
tion is  made  posterior  to  the  ganglion  of  Gasser,  and  to  the  anastomosing 
filaments  of  the  sympathetic  which  join  the  nerve  at  this  point;  but  if  the 
ganglion  be  divided,  these  effects  are  very  noticeable,  due  to  the  section  of 
the  sympathetic  filaments. 


108  HUMAN   PHYSIOLOGY. 

Function.  Gives  sensibility  to  all  parts  of  the  head  and  face  to  which 
it  is  distributed ;  through  the  small  root  endows  the  masticatory  muscles 
with  motion ;  through  fibres  from  the  sympathetic  governs  the  nutrition  of 
the  special  senses. 

7th  Pair.     Portio  Dura.     Facial  Nerve. 

Apparent  Origin.  From  the  groove  between  the  olivary  and  restiform 
bodies  at  the  lateral  portion  of  the  medulla  oblongata,  and  below  the  margin 
of  the  pons  Varolii. 

Deep  Origin.  From  a  nucleus  of  large  cells  in  the  floor  of  the  4th 
ventricle,  below  the  nucleus  of  origin  of  the  6th  pair,  with  which  it  is 
connected.  Some  filaments  are  traceable  to  the  lenticular  nucleus  of  the 
opposite  side.  Some  of  the  fibres  cross  the  median  line  and  decussate.  It 
is  intimately  associated  with  the  nerve  of  Wrisberg  at  its  origin. 

Distribution.  From  its  origin  the  facial  nerve  passes  into  the  internal 
auditory  meatus,  and  then,  in  company  with  the  nerve  of  Wrisberg,  enters 
the  aqueduct  of  Fallopius.  The  filaments  of  the  nerve  of  Wrisberg  are 
supplied  with  a  ganglion,  of  a  reddish  color,  having  nerve  cells.  These 
filaments  unite  with  those  of  the  root  of  the  facial,  to  form  a  common  trunk, 
which  emerges  at  the  stylo-mastoid  foramen. 

In  the  aqueduct  the  facial  gives  off  the  following  branches,  viz. : — 

1.  Large petrosal  nerve,  which  passes  forward  to  the  spheno-palatine,  or 
Meckel's  ganglion,  and  through  this  to  the  levator  palati  and  azygos  uvulae 
muscles,  which  receive  motor  influence  from  this  source. 

2.  Small  petrosal  nerve,  passing  to  the  otic  ganglion  and  thence  to  the 
tensor-tympani  muscle,  endowing  it  with  motion. 

3.  Tympanic  branch,  giving  motion  to  the  stapedius  muscle. 

4.  Chorda  tympani  nerve,  which  after  entering  the  posterior  .part  of  the 
tympanic   cavity,  passes   forward   between  the  malleus  and   incus  bones, 
through  the  Glasserian  fissure,  and  joins  the  lingual  branch   of  the  5th 
nerve.     It  is  then  distributed  to  the  mucous  membrane  of  the    anterior 
two-thirds  of  the  tongue  and  the  sub-maxillary  glands. 

After  emerging  from  the  stylo-mastoid  foramen,  the  facial  nerve  sends 
branches  to  the  muscles  of  the  ear,  the  occipito-frontalis,  the  digastric,  the 
palato-glossi,  and  palato-pharyngei ;  after  which  it  passes  through  the  parotid 
gland  and  divides  into  the  ternporo-fadal  and  cervico-facial  branches,  which 
are  distributed  to  the  superficial  muscles  of  the  face,  viz. ;  occipito-frontalis, 
corrugator  supercilii,  orbicularis  palpebrarum,  levator  labii  superioris  et 
alaeque  nasi,  buccinator,  levator  anguli  oris,  orbicularis  oris,  zygomatici, 
depressor  anguli  oris,  platysma  myoides,  etc. 


CRANIAL   NERVES.  109 

Properties.  Undoubtedly  a  motor  nerve  at  its  origin,  but  in  its  course 
receives  sensitive  filaments  from  the  5th  pair  and  the  pneumogastric. 

Irritation  of  the  nerve;  after  its  emergence  from  the  stylo-mastoid  fora- 
men, produces  convulsive  movements  in  all  the  superficial  muscles  of  the 
face.  Division  of  the  nerve  at  this  point  causes  paralysis  of  these  muscles 
on  the  side  of  the  section,  constituting  facial  paralysis ;  the  phenomena  o(f 
which  are,  a  relaxed  and  immobile  condition  of  the  same  side  of  the  face ; 
the  eyelids  remain  open,  from  paralysis  of  the  orbicularis  palpebrarum  ; 
the  act  of  winking  is  abolished ;  the  angle  of  the  mouth  droops,  and  saliva 
constantly  drains  away;  the  face  is  drawn  over  to  the  sound  side ;  the  face 
becomes  distorted  upon  talking  or  laughing ;  mastication  is  interfered  with, 
the  food  accumulating  between  the  gums  and  cheek,  from  paralysis  of  the 
buccinator  muscle;  fluids  escape  from  the  mouth  in  drinking;  articulation 
is  impaired,  the  labial  sounds  being  imperfectly  pronounced. 

Properties  of  the  branches  given  off  in  the  aqueduct  of  Fallopius.  The 
Large  petrosal,  when  irritated,  throws  the  levator  palati  and  azygos  uvulae 
muscles  into  contraction.  Paralysis  of  this  nerve,  from  deep-seated  lesions, 
produces  a  deviation  of  the  uvula  to  the  sound  side,  a  drooping  of  the  palate, 
and  an  inability  to  elevate  it. 

The  Small  petrosal  influences  hearing  by  animating  the  tensor  tympani 
muscle ;  when  paralyzed,  there  occurs  partial  deafness  and  an  increased 
sensibility  to  sonorous  impressions. 

The  Tympanitic  branch  animates  the  stapSdius  muscle,  and  influences 
audition. 

The  Chorda  tympani  influences  the  circulation  and  the  secretion  of 
saliva,  in  the  sub-maxillary  glands,  and  governs  the  sense  of  taste  in  the 
anterior  two-thirds  of  the  tongue.  Galvanization  of  the  chorda  tympani 
dilates  the  blood  vessels,  increases  the  quantity  and  rapidity  of  the  stream 
of  blood,  and  increases  the  secretion  of  saliva.  Division  of  the  nerve  is 
followed  by  contraction  of  the  vessels,  an  arrestation  of  the  secretion,  and 
a  diminution  of  the  sense  of  taste,  on  the  same  side. 

Function.  The  facial  is  the  nerve  of  expression,  and  coordinates  the 
muscles  employed  to  delineate  the  various  emotions,  influences  the  sense 
of  taste,  deglutition,  movements  of  the  uvula  and  soft  palate,  the  tension  of 
the  membrana  tympani,  and  the  secretions  of  the  sub-maxillary  and  parotid 
glands.  Indirectly  influences  smell,  hearing  and  vision. 

8th  Pair.     Portio  Mollis.     Auditory  Nerve. 

Apparent  Origin.  From  the  upper  and  lateral  portion  of  the  medulla 
oblongata,  just  below  the  margin  of  the  pons  Varolii. 


110  HUMAN   PHYSIOLOGY. 

Deep  Origin.  By  two  roots  from  the  floor  of  the  4th  ventricle,  each 
root  consisting  of  a  number  of  gray  filaments,  some  of  which  decussate  in 
the  median  line;  the  external  root  has  a  gangliform  enlargement  contain- 
ing fusiform  nerve  cells. 

Distribution.  The  two  roots  wind  around  the  restiform  bodies  and 
enter  the  internal  auditory  meatus,  and  divide  into  an  anterior  branch 
distributed  to  the  cochlea,  and  a  posterior  branch  distributed  to  the  vesti- 
bule and  semicircular  canals. 

Properties.  They  are  soft  in  consistence,  grayish  in  color,  consisting 
of  axis  cylinders  with  a  medullary  sheath  only;  they  are  not  sensible  to 
ordinary  impressions,  but  convey  the  impression  of  sound. 

Function.  Governs  the  sense  of  hearing.  Receives  and  conducts  to 
the  brain  the  impression  of  sound,  which  gives  rise  to  the  sensations  of 
hearing. 

gth  Pair.     Glosso-pharyngeal. 

Apparent  Origin.  Partly  from  the  medulla  oblongata  and  the  inferior 
peduncles  of  the  cerebellum. 

Deep  Origin.  From  the  lower  portion  of  the  gray  substance  in  the 
floor  of  the  4th  ventricle. 

This  nerve  has  two  ganglia ;  the  jugular  ganglion  includes  only  a  por- 
tion of  the  root  filaments ;  the  ganglion  of  Andersch  includes  all  the  fibres 
of  the  trunk.  • 

Distribution.  The  trunk  of  the  nerve  passes  downward  and  forward, 
receiving  near  the  ganglion  of  Andersch  fibres  from  the  facial  and  pneu- 
mogastric  nerves.  It  divides  into  two  large  branches,  one  of  which  is 
distributed  to  the  base  of  the  tongue,  the  other  to  the  pharynx.  In  its 
course  it  sends  filaments  to  the  otic  ganglion ;  a  tympanic  branch  which 
gives  sensibility  to  the  mucous  membrane  of  the  fenestra  rotunda,  fenestra 
ovalis,  and  Eustachian  tube;  lingual  branches  to  the  base  of  the  tongue; 
palatal  branches  to  the  soft  palate,  uvula  and  tonsils ;  pharyngeal  branches 
to  the  mucous  membrane  of  the  pharynx. 

Properties.  Irritation  of  the  roots  at  their  origin  calls  forth  evidences 
of  pain ;  it  is,  therefore,  a  sensory  nerve,  but  its  sensibility  is  not  so  acute 
as  that  of  the  trifacial.  Irritation  of  the  trunk  after  its  exit  from  the 
cranium  produces  contraction  of  the  muscles  of  the  palate  and  pharynx, 
due  to  the  presence  of  anastomosing  motor  fibres. 

Division  of  the  nerve  abolishes  sensibility  in  the  structures  to  which  it  is 
distributed,  and  impairs  the  sense  of  taste  in  the  posterior  third  of  the 
tongue  (see  Sense  of  Taste). 


CRANIAL  NERVES.  Ill 

Function.      Governs  sensibility  of  pharynx,  presides  partly  over  the 
sense  of  taste,  and  controls  reflex  movements  of  deglutition  and  vomiting. 


roth  Pair.     Pneumogastric.     Par  Vagum. 

Apparent  Origin.  From  the  lateral  side  of  the  medulla  oblongata, 
just  behind  the  olivary  body. 

Deep  Origin.  In  the  gray  nuclei  in  the  lower  half  of  the  floor  of  the 
4th  ventricle,  and  in  the  substance  of  the  restiform  body.  Some  filaments 
are  traced  along  the  restiform  tract,  toward  the  cerebellum,  and  others  to  the 
median  line  of  the  floor  of  the  4th  ventricle,  where  many  of  them  decussate. 

This  nerve  has  two  ganglia ;  one  in  the  jugular  foramen,  called  the  gan- 
glion of  the  root,  and  another  outside  of  the  cranial  cavity  on  the  trunk, 
the  ganglion  of  the  trunk. 

Distribution.  The  filaments  from  the  root  unite  to  form  a  single  trunk, 
which  leaves  the  cavity  of  the  cranium,  through  the  jugular  foramen,  in 
company  with  the  spinal  accessory  and  glosso-pharyngeal.  It  soon  receives 
an  anastomotic  branch  from  the  spinal  accessory,  and  afterward  branches 
from  the  facial,  the  hypoglossal  and  the  anterior  branches  of  the  two  upper 
cervical  nerves. 

As  the  nerve  passes  down  the  neck  it  sends  off  the  following  main 
branches: — 

1.  Pharyngeal  nerves,  which  assist  in  forming  the  pharyngeal  plexus, 
which  is  distributed  to  the  mucous  membrane  and  muscles  of  the  pharynx. 

2.  Superior  laryngeal  nerve,  which  enters  the  larynx  through  the  thyro- 
hyoid  membrane,  and  is  distributed  to  the  mucous  membrane  lining  the 
interior  of  the  larynx,  and  to  the  crico-thyroid  muscle  and  the  inferior  con- 
strictor of  the  pharynx.     The  "depressor  nerve"  found  in  the  rabbit,  is 
formed  by  the  union  of  two  branches,  one  from  the  superior  laryngeal,  the 
other  from  the  main  trunk ;  it  passes  downward  to  be  distributed  to  the 
heart. 

3.  Inferior  laryngeal,  which  sends  its   ultimate   branches   to   all   the 
intrinsic  muscles  of  the  larynx  except  the  crico-thyroid,  and  to  the  inferior 
constrictor  of  the  pharynx. 

4.  Cardiac  branches  given  off  from  the  nerve  throughout  its  course,  which 
unite  with  the  sympathetic  fibres  to  form  the  cardiac  plexus,  to  be  distributed 
to  the  heart. 

5.  Pulmonary  branches,  which  form  a  plexus  of  nerves  and  are  dis- 
tributed to  the  bronchi  and  their  ultimate  terminations,  the  lobules  and  air 
cells. 


112  HUMAN    PHYSIOLOGY. 

From  the  right  pneumogastrlc  nerve  branches  are  distributed  to  the 
mucous  membrane  and  muscular  coats  of  the  stomach  and  intestines,  to  the 
liver,  spleen,  kidneys,  and  supra-renal  capsules. 

Properties.  At  its  origin  the  pneumogastric  nerve  is  sensory,  as  shown 
by  direct  irritation  or  galvanization,  though  its  sensibility  is  not  very 
marked.  In  its  course  exhibits  motor  properties,  from  anastomosis  with 
motor  nerves. 

The  Pharyngeal  branches  assist  in  giving  sensibility  to  the  mucous 
membrane  of  the  pharynx,  and  influence  reflex  phenomena  of  deglutition 
through  motor  fibres  which  they  contain,  derived  from  the  spinal 
accessory. 

The  Superior  laryngeal  nerve  endows  the  upper  portion  of  the  larynx 
with  sensibility ;  protects  it  from  the  entrance  of  foreign  bodies ;  by  con- 
ducting impressions  to  the  medulla,  excites  the  reflex  movements  of  deglu- 
tition and  respiration;  through  the  motor  filaments  it  contains  produces 
contraction  of  the  crico-thyroid  muscle. 

Division  of  the  "  Depressor  nerve"  and  galvanization  of  the  central 
end,  retards  and  even  arrests  the  pulsations  of  the  heart,  and  by  depressing 
the  vasomotor  centre  diminishes  the  pressure  of  blood  in  the  large  vessels, 
by  causing  dilatation  of  the  intestinal  vessels  through  the  splanchnic 
nerves. 

The  Inferior  laryngeal  contains,  for  the  most  part,  motor  fibres  from 
the  spinal  accessory.  When  irritated  produces  movement  in  the  laryn- 
geal muscles.  When  divided,  is  followed  by  paralysis  of  these  muscles, 
except  the  crico-thyroid,  impairment  of  phonation,  and  an  embarrassment 
of  the  respiratory  movements  of  the  larynx,  and  finally  death,  from  suffo- 
cation. 

The  Cardiac  branches,  through  filaments  derived  from  the  spinal  acces- 
sory, exert  a  direct  inhibitory  action  upon  the  heart.  Division  of  the 
pneumogastrics  in  the  neck  increases  the  frequency  of  the  heart's  action. 
Galvanization  of  the  peripheral  ends  diminishes  the  heart's  pulsation,  and, 
if  sufficiently  powerful,  paralyzes  it  in  diastole. 

The  Pulmonary  branches  give  sensibility  to  the  bronchial  mucous 
membrane,  and  govern  the  movements  of  respiration.  Division  of  both 
pneumogastrics  in  the  neck  diminishes  the  frequency  of  the  respiratory 
movements,  falling  as  low  as  four  to  six  per  minute ;  death  usually  occurs 
in  from  five  to  eight  days.  Feeble  galvanization  of  the  central  ends  of  the 
divided  nerves  accelerates  respiration  ;  powerful  galvanization  retards,  and 
may  even  arrest  the  respiratory  movements. 

The   Gastric  branches  give  sensibility  to  the  mucous  coat,  and  through 


CRANIAL   NERVES.  113 

sympathetic  filaments,  which  join  the  pneumogastrics  high  up  in  the  neck, 
give  motion  to  the  muscular  coat  of  the  stomach.  They  influence  the 
secretion  of  gastric  juice,  aid  the  process  of  digestion  and  absorption  from 
the  stomach. 

The  Hepatic  branches,  probably  through  anastomosing  sympathetic  fila- 
ments, influence  the  secretion  of  bile,  and  the  glycogenic  function  of  the 
liver;  division  of  the  pneumogastrics  in  the  neck  produces  congestion  of 
the  liver,  diminishes  the  density  of  the  bile,  and  arrests  the  glycogenic 
function ;  galvanization  of  the  central  ends  exaggerates  the  glycogenic 
function,  and  makes  the  animal  diabetic. 

The  Intestinal  branches  give  sensibility  and  motion  to  the  small  intes- 
tines, and  when  divided,  purgatives  generally  fail  to  produce  purgation. 

Function.  A  great  sensitive  nerve,  which,  through  anastomotic  fila- 
ments from  motor  sources,  influences  deglutition,  the  action  of  the  heart, 
the  circulatory  and  respiratory  systems,  voice,  the  secretions  of  the  stomach, 
intestines,  and  various  glandular  organs. 

nth  Pair.     Spinal  Accessory. 
Apparent  Origin.     By  two  sets  of  filaments: — 

1.  A  bulbar  or  medullary  set,  four  or  five  in  number,  from  the  lateral  or 
motor  tract  of  the  lower  half  of  the  medulla  oblongata,  below  the  origin  of 
the  pneumogastric. 

2.  A  spinal  set,  from  six  to  eight  in  number,  from  the  lateral  portion  of 
the  spinal  cord,  between  the  anterior  and  posterior  roots  of  the  upper  four  or 
five  cervical  nerves. 

Deep  Origin.  The  medtdlary  portion  arises  in  a  nucleus  in  the  lower 
half  of  the  floor  of  the  4th  ventricle,  common  to  the  pneumogastric  and 
glosso  pharyngeal  nerves.  The  spinal  portion  has  its  origin  in  an  elongated 
nucleus  lying  along  the  external  surface  of  the  anterior  cornua  of  the  spinal 
cord,  extending  down  to  the  5th  cervical  vertebra. 

Distribution.  From  this  origin  the  fibres  unite  to  form  a  main  trunk, 
which  enters  the  cranial  cavity  through  the  foramen  magnum,  where  it  is 
at  times  joined  by  fibres  from  the  posterior  roots  of  the  two  upper  cervical 
nerves,  and  sends  filaments  to  the  ganglion  of  the  root  of  the  pneumo- 
gastric. After  emerging  from  the  cranial  cavity  through  the  jugular  fora- 
men, it  sends  a  branch  to  the  pneumogastric,  and  receives  others  in  return, 
and  also  from  the  2d,  3d  and  4th  cervical  nerves.  It  divides  into  two 
branches:  (i)  An  internal  or  anastomotic  branch,  made  up  of  filaments 
coming  principally  from  the  medulla  oblongata,  and  is  distributed  to  the 


114  HUMAN  PHYSIOLOGY. 

muscles  of  the  pharynx  through  the  pharyngeal  nerves  coming  from  the 
pneumogastric ;  to  all  the  muscles  of  the  larynx,  except  the  crico-thyroid 
through  the  inferior  laryngeal  nerve;  to  the  heart,  by  filaments  which 
reach  it  through  the  pneumogostric  nerve.  (2)  An  external  branch,  which 
is  distributed  to  the  sterno-cleido-mastoid  and  trapezius  muscles ;  these 
muscles  also  receiving  filaments  from  the  cervical  nerves. 

Properties.  At  its  origin  it  is  a  purely  motor  nerve,  but  in  its  course 
exhibits  some  sensibility  from  anastomosing  fibres. 

Destruction  of  the  medullary  root,  by  tearing  it  from  its  attachment  by 
means  of  forceps,  impairs  the  action  of  the  muscles  of  deglutition,  and 
destroys  the  power  of  producing  vocal  sounds  by  paralysis  of  the  laryngeal 
muscles,  without,  however,  interfering  with  the  respiratory  movements  of 
the  larynx  ;  these  being  controlled  by  other  motor  nerves.  The  normal 
rate  of  movement  of  the  heart  is  also  impaired  by  destruction  of  the 
medullary  root. 

Irritation  of  the  external  branch  throws  the  trapezius  andsterno-mastoid 
muscles  into  convulsive  movements,  though  section  of  the  nerve  does  not 
produce  complete  paralysis,  as  they  are  also  supplied  with  motor  influence 
from  the  cervical  nerves.  The  sterno-mastoid  and  trapezius  muscles  per- 
form movements  antagonistic  to  those  of  respiration,  fixing  the  head,  neck 
and  upper  part  of  the  thorax,  and  delaying  the  expiratory  movement  during 
the  acts  of  pushing,  pulling,  straining,  etc.,  and  in  the  production  of  a  pro- 
longed vocal  sound,  as  in  singing.  When  the  external  branch  alone  is 
divided,  in  animals,  they  experience  shortness  of  breath  during  exercise, 
from  a  want  of  coordination  of  the  muscles  of  the  limbs  and  respiration  ; 
and  while  they  can  make  a  vocal  sound,  it  cannot  be  prolonged. 

Function.  Governs  phonation  by  its  influence  upon  the  vocal  move- 
ments of  the  glottis ;  influences  the  movements  of  deglutition,  inhibits  the 
action  of  the  heart  and  controls  certain  respiratory  movements  associated 
with  sustained  or  prolonged  muscular  efforts  and  phonation. 

I2th  Pair.     Hypoglossal  or  Sublingual. 

Apparent  Origin.  By  two  groups  of  filaments  from  the  medulla  ob- 
longata,  in  the  grooves  between  the  olivary  body  and  the  anterior  pyramid. 

Deep  Origin.  From  the  hypoglossal  nucleus  situated  deeply  in  the 
substance  of  the  medulla,  on  a  level  with  the  lowest  portion  of  the  floor,  of 
the  4th  ventricle;  some  decussating  filaments  have  been  traced  to  a  higher 
encephalic  centre. 

Distribution.     The   trunk   formed   by  a  union   of  the  root  filament 


CEREBRO-SPINAL  AXIS.  115 

passes  out  of  the  cranial  cavity  through  the  anterior  condyloid  foramen, 
occasionally  receiving  a  filament  from  the  lateral  and  posterior  portion  of 
the  medulla  oblongata.  After  emerging  from  the  cranium,  it  sends  filaments 
to  the  sympathetic  and  pneumogastric ;  it  anastomoses  with  the  lingual 
branch  of  the  5th  pair,  and  receives  and  sends  filaments  to  the  upper  cer- 
vical nerves.  The  nerve  is  finally  distributed  to  the  sterno-hyoid,  sterno- 
thyroid,  omo-hyoid,  thyro-hyoid,  stylo-glossi,  hyo-glossi,  genio-hyoid,genio- 
hyo-glossi,  and  the  intrinsic  muscles  of  the  tongue. 

Properties.  A  purely  motor  nerve  at  its  origin,  but  derives  sensibility 
outside  the  cranial  cavity,  from  anastomosis  with  the  cervical,  pneumo- 
gastrtc  and  5th  nerves. 

Irritation  of  the  nerve  gives  rise  to  convulsive  movements  of  the  tongue 
and  slight  evidences  of  sensibility. 

Division  of  the  nerve  abolishes  all  movements  of  the  tongue,  and  inter- 
feres considerably  with  the  act  of  deglutition. 

When  the  hypoglossal  nerve  is  involved  in  hemiplegia,  the  tip  of  the 
tongue  is  directed  to  the  paralyzed  side  when  the  tongue  is  protruded; 
due  to  the  unopposed  action  of  the  genio-hyo-glossus  on  the  sound  side. 

Articulation  is  considerably  impaired  in  paralysis  of  this  nerve;  great 
difficulty  being  experienced  in  the  pronunciation  of  the  consonantal 
sounds. 

Mastication  is  performed  with  difficulty,  from  inability  to  retain  the  food 
between  the  teeth  until  it  is  completely  triturated. 

Function.  Governs  all  the  movements  of  the  tongue  and  influences  the 
functions  of  mastication,  deglutition  and  articulate  language. 


CEREBRO-SPINAL  AXIS. 

The  Cerebro-Spinal  Axis  consists  of  the  spinal  cord,  medulla  oblon- 
gata, pons  Varolii,  cerebellum  and  cerebrum,  exclusive  of  the  spinal  and 
cranial  nerves.  It  is  contained  within  the  cavities  of  the  cranium  and 
spinal  column,  and  surrounded  by  three  membranes,  the  dura  mater, 
arachnoid  and  pia  mater,  which  protect  it  from  injury  and  supply  it  with 
blood  vessels. 

The  Brain  and  Spinal  Cord  are  composed  of  both  white  fibres  and 
collections  of  gray  cells,  and  are,  therefore,  to  be  regarded  as  conductors  of 
impressions  and  motor  impulses,  as  well  as  generators  of  nerve  force. 


116  HUMAN  PHYSIOLOGY. 

MEMBRANES. 

The  Dura  Mater,  the  most  external  of  the  three,  is  a  tough  membrane, 
composed  of  white  fibrous  tissue,  arranged  in  bundles,  which  interlace  in 
every  direction.  In  the  cranial  cavity  it 'lines  the  inner  surface  of  the 
bones,  and  is  attached  to  the  edge  of  the  foramen  magnum;  sends  processes 
inward,  forming  the  falx  cerebri,  falx  cerebelli,  and  tentorium  cerebelli, 
supporting  and  protecting  parts  of  the  brain.  In  the  spinal  canal  it  loosely 
invests  the  cord,  and  is  separated  from  the  walls  of  the  canal  by  areolar 
tissue. 

The  Arachnoid,  the  middle  membrane,  is  a  delicate  serous  structure 
which  envelopes  the  brain  and  cord,  forming  the  visceral  layer,  and  is  then 
reflected  to  the  inner  surface  of  the  dura  mater,  forming  the  parietal  layer. 
Between  the  two  layers  there  is  a  small  quantity  of  fluid  which  prevents 
friction  by  lubricating  the  two  surfaces. 

The  Pia  Mater,  the  most  internal  of  the  three,  composed  of  areolar 
tissue  and  blood  vessels,  covers  the  entire  surface  of  the  brain  and  cord,  to 
which  it  is  closely  adherent,  dipping  down  between  the  convolutions  and 
fissures.  It  is  exceedingly  vascular,  sending  small  blood  vessels  some  dis- 
tance into  the  brain  and  cord. 

The  Cerebro-spinal  Fluid  occupies  the  sub-arachnoid  space,  and  the 
general  ventricular  cavities  of  the  brain,  which  communicate  by  an  opening, 
the  foramen  of  Magendie,  in  the  pia  mater,  at  the  lower  portion  of  the  4th 
ventricle.  This  fluid  is  clear,  transparent,  alkaline,  possesses  a  salt  taste  and 
a  low  specific  gravity;  it  is  composed  largely  of  water,  traces  of  albumen, 
glucose  and  mineral  salts.  It  is  secreted  by  the  pia  mater;  the  quantity  is 
estimated  from  two  to  four  fluid  ozs. 

The  function  of  the  cerebro-spinal  fluid  is  to  protect  the  brain  and  cord, 
by  preventing  concussion  from  without ;  by  being  easily  displaced  into  the 
spinal  canal,  prevents  undue  pressure  and  insufficiency  of  blood  to  the 
brain. 

SPINAL  CORD. 

The  Spinal  Cord  varies  from  16  to  18  inches  in  length;  is  half  an  inch 
in  thickness,  weighs  i^  oz.,  and  extends  from  the  atlas  to  the  2d  lumbar 
vertebra,  terminating  in  the  filum  terminale.  It  is  cylindrical  in  shape, 
and  presents  an  enlargement  in  the  lower  cervical  and  lower  dorsal  regions, 
corresponding  to  the  origin  of  the  nerves  which  are  distributed  to  the 
upper  and  lower  extremities.  The  cord  is  divided  into  two  lateral  halves 


SPINAL  CORD. 


117 


by  the  anterior  and  posterior  fissures.  It  is  composed  of  both  white  or 
fibrous  and  gray  or  vesicular  matter,  the  former  occupying  the  exterior  of 
the  cord,  the  latter  the  interior,  where  it  is  arranged  in  the  form  of  two 
crescents,  one  in  each  lateral  half,  united  together  by  the  central  mass,  the 
gray  commissure ;  the  white  matter  being  united  in  front  by  the  white 
commissure. 

Structure  of  the  White  Matter.  The  white  matter  surrounding  each 
lateral  half  of  the  cord  is  made  up  of  nerve  fibres,  some  of  which  are  con- 
tinuations of  the  nerves  which  enter  the  cord,  while  others  are  derived 
from  different  sources.  It  is  subdivided  into:  (i)  An  Anterior  column, 
comprising  that  portion  between  the  anterior  roots  and  the  anterior  fissure, 
which  is  again  subdivided  into  two  parts  :  (#)  an  inner  portion,  bordering 
the  anterior  median  fissure,  the  direct  pyramidal  tract,  or  column  of  Turck, 
containing  motor  fibres  which  do  not  decussate,  and  which  extends  as  far 
down  as  the  middle  of  the  dorsal  region  ;  (£)  an  outer  portion,  surrounding 
the  anterior  cornua,  known  as  the  anterior  root  zone,  composed  of  short 
longitudinal  fibres  which  serve  to  connect  together  different  segments  of 
the  spinal  cord.  (2)  A  Lateral 
column,  the  portion  between 
the  anterior  and  posterior  roots, 
which  is  divisible  into  (a)  the 
crossed  pyramidal  tract,  occupy- 
ing the  posterior  portion  of  the 
lateral  column,  and  containing 
all  those  fibres  of  the  motor  tract 
which  have  decussated  at  the 
medulla  oblongata ;  it  is  com- 
posed of  longitudinally  running 
fibres  which  are  connected  with 
the  multipolar  nerve  cells  of  the 
anterior  cornua ;  (b}  the  direct 
cerebellar  tract,  situated  upon 
the  surface  of  the  lateral  column, 
consisting  of  longitudinal  fibres 
which  terminate  in  the  cere- 
bellum ;  it  first  appears  in  the 
lumbar  region,  and  increases  as 
it  passes  upward ;  (c]  the  anterior  tract,  lying  just  posterior  to  the  anterior 
cornua.  (3)  A  Posterior  column,  the  portion  included  between  the  posterior 
roots  and  the  posterior  fissure,  also  divisible  into  two  portions,  (a)  an  inner 


SCHEME   OF    THE    CONDUCTING   PATHS    IN  THE 
SPINAL  CORD  AT  THE  3D  DORSAL  NERVE. 

The  black  part  is  the  gray  matter,  v,  anterior, 
hw,  posterior,  root ;  a,  direct,  and  g,  crossed, 
pyramidal  tracts  ;  b,  anterior  column,  ground 
bundle ;  c,  Coil's  column ;  d,  postero-exter- 
nal  column  ;  e  and  f,  mixed  lateral  paths ;  h, 
direct  cerebellar  tracts. — Landois. 


118  HUMAN   PHYSIOLOGY. 

portion,  the  postero-internal  column,  or  the  column  of  Goll,  bordering  the 
posterior  median  fissure,  and  (<5)  an  external  portion,  the  poster o- external 
column,  the  column  of  Burdach,  lying  just  behind  the  posterior  roots. 
They  are  composed  of  long  and  short  commissural  fibres  which  connect 
together  different  segments  of  the  spinal  cord. 

Structure  of  the  Gray  Matter.  The  gray  matter,  arranged  in  the 
form  of  two  crescents,  presents  an  anterior  and  posterior  horn.  It  is  made 
up  of  a  delicate  network  of  fine  nerve  fibres  (axis  cylinders),  supported  by 
a  connective  tissue  frame  work  of  nucleated  nerve  cells,  which  in  the  anterior 
horns  are  large  and  multipolar,  and  connected  with  the  anterior  roots  of 
spinal  nerves  ;  in  the  posterior  horns  the  nerve  cells  are  smaller,  and  situated 
along  the  inner  margin,  and  in  the  caput  cornu.  Small  cells  are  also  found 
in  the  posterior  vesicular  columns,  and  in  the  intermediary  lateral  tract. 


SPINAL    NERVES. 

Origin.  The  spinal  nerves  are  thirty-one  in  number  on  each  side  of  the 
spinal  cord,  and  arise  by  two  roots,  an  anterior  and  .posterior,  from  the 
anterior  and  posterior  aspects  of  the  cord  respectively :  the  posterior  roots 
present  near  their  emergence  from  the  cord  a  small  ganglionic  enlargement ; 
outside  of  the  spinal  canal  the  two  roots  unite  to  form  a  main  trunk,  which 
is  ultimately  distributed  to  the  skin,  muscles  and  viscera. 

The  Function  of  the  Anterior  Roots  is  to  transmit  motor  impulses 
from  the  centres  outward  to  the  periphery.  Irritation  of  these  roots,  from 
whatever  cause,  excites  convulsive  movements  in  the  muscles  to  which  they 
are  distributed ;  disease  or  division  of  these  roots  induces  a  condition  of 
paresis  or  paralysis. 

The  Function  of  the  Posterior  Roots  is  to  transmit  the  impressions 
'made  upon  the  periphery  to  the  centres  in  the  spinal  cord,  where  they 
excite  motor  impulses ;  or  to  the  brain,  in  which  they  are  translated  into 
conscious  sensations.  Irritation  of  these  roots  gives  rise  to  painful  sensa- 
tions ;  division  of  the  roots  abolishes  all  sensation  in  the  parts  to  which 
they  are  distributed. 

The  ganglion  on  the  posterior  root  influences  the  nutrition  of  the  sensory 
nerve;  for  if  the  nerve  be  separated  from  the  ganglion,  it  undergoes 
degeneration  in  the  course  of  a  few  days,  in  the  direction  in  which  it 
carries  impressions,  i.  e.,  from  the  periphery  to  the  centres;  if  the  nerve  be 
divided  between  the  ganglion  and  the  cord,  the  central  end  only  undergoes 


SPINAL   NERVES.  119 

degeneration.  The  nutrition  of  the  anterior  root  is  governed  by  nerve  cells 
in  the  gray  matter  of  the  cord ;  for  if  these  cells  undergo  atrophy,  or  if  the 
nerve  be  divided,  it  undergoes  degeneration  outward. 


COURSE  OF  THE  ANTERIOR  AND  POSTERIOR  ROOTS. 

The  Anterior  Roots  pass  through  the  anterior  columns,  horizontally, 
in  straight  and  distinct  bundles,  and  enter  the  anterior  cornuae,  where  they 
diverge  in  four  directions,  (i)  Many  become  connected  with  the  prolon- 
gations of  the  multipolar  nerve  cells.  (2)  Others  leave  the  gray  matter, 
pass  through  the  anterior  white  commissure,  and  enter  the  anterior  columns 
of  the  opposite  side.  (3)  A  considerable  number  enter  the  lateral  columns 
of  the  same  side,  through  which  they  pass  to  the  medulla  oblongata,  where 
they  decussate  and  finally  terminate  in  the  corptts  striatum  of  the  opposite 
side.  (4)  Others  traverse  the  gray  matter  horizontally,  and  come  into 
relation  with  the  posterior  roots. 

The  Posterior  Roots  enter  the  posterior  horns  of  the  gray  matter  (l) 
through  the  substantia  gelatinosa,  (2)  through  the  posterior  columns;  of 
the  former,  some  bend  upward  and  downward,  and  become  connected 
with  the  anterior  cornuae ;  others  pass  through  the  posterior  commissure  to 
the  opposite  side;  of  the  latter,  fibres  pass  into  the  gray  matter,  to  the 
posterior  vesicular  columns,  passing  obliquely  through  the  posterior  white 
columns  upward  and  downward  for  some  distance,  and  enter  the  gray 
matter  at  different  heights. 

Decussation  of  Motor  and  Sensory  Fibres.  The  Motor  fibres, 
which  conduct  volitional  impulses  from  the  brain  outward  to  the  anterior 
cornuae,  arise  in  the  motor  centres  of  the  cerebrum ;  they  then  pass  down- 
ward through  the  corona  radiata,  the  internal  capsule,  the  inferior  portions 
of  the  crura  cerebri,  the  pons  Varolii,  to  the  medulla  oblongata,  where  the 
motor  tract  of  each  side  divides  into  two  portions,  viz  :  I .  The  larger, 
containing  91  to  97  per  cent,  of  the  fibres,  which  decussates  at  the  lower 
border  of  the  medulla  and  passes  down  in  the  lateral  column  of  the  oppo- 
site side,  and  constitutes  the  crossed  pyramidal  tract.  2.  The  smaller, 
containing  3  to  9  per  cent,  of  the  fibres,  does  not  decussate,  but  passes  down 
the  anterior  column  of  the  same  side,  and  constitutes  the  direct  pyramidal 
tract,  or  the  column  of  Tiirck.  Some  of  the  motor  fibres  of  these  two 
tracts,  after  entering  the  anterior  cornuae  of  the  gray  matter,  become  con- 
nected with  the  large  multipolar  nerve  cells,  while  others  pass  directly  into 
the  anterior  roots.  Through  this  decussation  each  half  of  the  brain  governs 
the  muscular  movements  of  the  opposite  side  of  the  body. 


120 


HUMAN   PHYSIOLOGY. 
FIG.  32. 


DIAGRAM    SHOWING   THE   COURSE,  THROUGH    THE   SPINAL   CORD,    OF   THE    MOTOR   AND 
SENSORY    NERVE    FIBRES. 

B  and  B'  represent  the  right  and  left  hemispheres  of  the  brain,  from  which  the  motor 
fibres  take  their  origin,  and  in  which  the  sensory  fibres  terminate.  The  motor  tract 
from  the  right  side  l  passes  down  through  the  crus,  through  the  pons  to  the  medulla 
oblongata,  where  it  divides  into  two  portions  :  ist,  the  larger  portion,  ninety-seven 
per  cent.,  crosses  over  to  the  opposite  side  of  the  cord  and  passes  down  through  the 
lateral  column.  It  gives  off  fibres  at  different  levels,  which  pass  into  the  gray  matter 
and  become  connected  with  the  muscles,  M,  through  the  multipolar  cells  ;  the  smaller 
Portion,  three  per  cent.,  does  not  cross  over,  but  descends  on  the  same  side  of  the 
cord  in  the  anterior  column  and  supplies  the  muscles,  m.  The  same  is  true  for  the 
motor  tract  for  the  left  hemisphere. 

The  sensory  fibres  from  the  left  side  of  the  body  enter  the  gray  matter  through  the 
posterior  roots.  They  then  cross  over  at  once  to  the  opposite  side  of  the  cord  and 
ascend  to  the  hemisphere  partly  in  the  gray  matter,  partly  in  the  posterior  column. 
The  same  is  true  for  the  sensory  nerves  of  the  right  side  of  the  body. 


PROPERTIES   OF   THE  SPINAL  CORD.  121 

The  Sensory  fibres,  which  convey  the  impression  made  upon  the  peri- 
phery to  the  cord  and  brain,  pass  into  the  cord  through  the  posterior  roots 
of  spinal  nerves;  they  then  diverge  and  enter  the  gray  matter  at  different 
levels,  and  at  once  decussate,  passing  to  the  opposite  side  of  the  gray 
matter.  The  sensory  tract  passes  upward,  through  the  cord,  the  medulla, 
pons  Varolii,  the  superior  portion  of  the  crura  cerebri,  the  posterior  third 
of  the  internal  capsule,  to  the  sensory  perceptive  centre,  located  in  the 
hippocampus  major  and  unciate  convolution  (Ferrier).  Through  this  decus- 
sation  each  half  of  the  brain  governs  the  sensibility  of  the  opposite  half 
of  the  body. 

Properties  of  the  Spinal  Cord.  Irritation  applied  directly  to  the 
antero-lateral  white  columns  produces  muscular  movements  but  no  pain  ; 
they  are,  therefore,  excitable  but  insensible. 

The  surface  of  the  posterior  columns  is  very  sensitive  to  direct  irritation, 
especially  near  the  origin  of  the  posterior  roots  ;  less  so  toward  the  posterior 
median  fissure.  The  sensibility  is  due,  however,  not  to  its  own  proper 
fibres,  but  to  the  fibres  of  the  posterior  root  which  traverse  it. 

Division  of  the  antero-lateral  columns  abolishes  all  power  of  voluntary 
movement  in  the  lower  extremities. 

Division  of  i\\e  posterior  columns  impairs  the  power  of  muscular  coordi- 
nation, such  as  is  witnessed  in  locomotor  ataxia. 

The  gray  matter  is  probably  both  insensible  and  inexcitable  under  the 
influence  of  direct  stimulation. 

A  transverse  section  of  one  lateral  half  of  the  cord  produces  : — 

(1)  On  the  same  side,  paralysis  of  voluntary  motion  and  a  relative  or 
absolute  elevation  of  temperature  and  an  increased  flow  of  blood  in  the 
paralyzed  parts  ;  hypersesthesia  for  the  sense  of  contact,  tickling,  pain  and 
temperature. 

(2)  On  the  opposite  side,  complete  anaesthesia  as  regards  contact,  and 
tickling  and  temperature,  in  the  part's  corresponding  to  those  which  are 
paralyzed  in  the  opposite  side.     Complete  preservation  of  voluntary  power 
and  of  the  muscular  sense. 

A  vertical  section  through  the  middle  of  the  gray  matter  results  in  the 
loss  of  sensation  on  both  sides  of  the  body  below  the  section,  but  no  loss  of 
voluntary  power. 


122  HUMAN    PHYSIOLOGY. 

FUNCTIONS  OF  THE  SPINAL  CORD, 

1.  As  a  Conductor.     The  Lateral  columns,  particularly  the  posterior 
portions,  the  "  pyramidal  tracts,"  and  the  columns  of  Tiirck,  are  the  chan- 
nels through  which  pass  the  voluntary  motor  impulses  from  the  brain  to  the 
large  multipolar  nerve  cells  in  the  anterior  cornuae  of  gray  matter,  and 
through  them  become  connected  with  the  anterior  roots  which  transmit  the 
motor  stimuli  to  the  muscles. 

The  Anterior  columns,  especially  the  portion  surrounding  the  anterior 
cornuae,  the  "  anterior  radicular  zones,"  are  composed  of  short  longitudinal 
commissural  fibres,  which  serve  to  connect  together  different,  segments  of 
the  spinal  cord,  a  condition  required  for  the  coordination  of  muscular 
movements. 

The  Posterior  columns  are  composed  of  short  and  long  commissural 
fibres  which  connect  together  different  segments  of  the  cord.  They  are 
insensible  to  direct  irritation,  but  aid  in  the  coordination  of  muscular  move- 
ments in  walking,  standing,  running,  etc.  Degeneration  of  the  posterior 
columns  gives  rise  to  the  lack  of  muscular  coordination  observed  in  loco- 
motor  ataxia. 

The  Gray  matter,  and  especially  that  portion  immediately  surrounding 
the  central  canal,  transmits  the  sensory  nerve  fibres  from  the  posterior  roots 
up  to  the  brain.  Decussation  of  the  sensory  fibres  takes  place  throughout 
the  whole  length  of  the  gray  matter. 

The  Multipolar  cells  of  the  anterior  cornua  are  connected  with  the 
generation  and  transmission  of  motor  impulses  outward;  are  centres  for 
reflex  movements;  are  the  trophic  centres  for  the  motor  nerves  and  muscu- 
lar fibres  to  which  they  are  distributed.  The  anterior  roots  give  passage 
to  the  vaso-constrictor  and  vaso  dilator  fibres  which  exert  an  influence 
upon  the  calibre  of  the  blood  vessels.  Complete  destruction  of  the  anterior 
horns  is  followed  by  a  paralysis  of  motion,  degeneration  of  the  anterior 
roots,  atrophy  of  muscles  and  bones,  and  an  abolition  of  reflex  move- 
ments. 

2.  As  an  Independent  Nerve  Centre. 

The  spinal  cord,  by  virtue  of  its  contaiaing  ganglionic  nerve  matter,  is 
capable  of  transforming  impressions  made  upon  the  centripetal  nerves  into 
motor  impulses,  which  are  reflected  outward  through  centrifugal  nerves  to 
muscles,  producing  movements.  These  reflex  movements  taking  place 
through  the  gray  matter,  are  independent  of  sensation  and  volition. 

The  mechanism  involved  in  every  reflex  act  is  a  sentient  surface,  a  sensory 
nerve,  a  nerve  centre,  a  motor  nerve  and  muscle. 


FUNCTIONS   OF  THE  SPINAL  CORD.  123 

The  reflex  excitability  of  the  cord  may  be — 

1.  Increased  by  disease   of  the  lateral  columns,  the  administration  of 
strychnia,  and  in  frogs,  by  a  separation  of  the  cord  from  the  brain,  the  latter 
apparently  exerting  an  inhibitory  influence  over  the  former  and  depressing 
its  reflex  activity. 

2.  Inhibited  \yy  destructive  lesions  of  the  cord,  e.g.,  locomotor  ataxia, 
atrophy  of  the  anterior  cornuae,  the  administration  of  various  drugs,  and,  in 
the  frog,  by  irritation  of  certain  regions  of  the  brain.     When  the  cerebrum 
alone  is  removed  and  the  optic  lobes  stimulated,  the  time  elapsing  between 
the  application  of  an  irritant  to  a  sensory  surface  and  the  resulting  movement 
will  be  considerably  prolonged.     The   optic   lobes  (Setchenow's  centre) 
apparently  generating  impulses  which,  descending  the  cord,  retard  its  reflex 
movements. 

All  movements  taking  place  through  the  nervous  system,  are  of  this  reflex 
character,  and  may  be  divided  into  excito-motor,  sensori-motor,  and  idea- 
motor. 

Classification  of  Reflex  Movements.  (Kiiss  )  They  may  be  divided 
into  four  groups,  according  to  the  route  through  which  the  centripetal  and 
centrifugal  impulses  pass. 

1.  Those  normal  reflex  acts,  e.g.,  deglutition,  coughing,  sneezing,  walk- 
ing, etc.,  pathological   reflex  acts,  e.  g.,  tetanus,  vomiting,  epilepsy,  which 
take  place  both  centripetally  and  centrifugally,  through  spinal  nerves. 

2.  Reflex  acts  which  take  place  in  a  centripetal  direction  through  a 
cerebro  spinal  sensory  nerve,  and  in  a  centrifugal  direction  through  a  sym- 
pathetic motor  nerve,  usually  a  vasomotor  nerve,  e.g.,  the  normal  reflex 
acts,  which  give  rise  to  most  of  the  secretions,  pallor  and  blushing  of  the 
skin,  certain  movements  of  the  iris,  certain  modifications  in  the  beat  of  the 
heart;  the  pathological,  which,  on  account  of  the  difficulty  in  explaining 
their  production,  are  termed  metaslatic ',  e.g.,  ophthalmia,  coryza,  orchitis, 
which  depend  on  a  reflex  hypersemia;  amaurosis,  paralysis,  paraplegia,  etc., 
due  to  a  reflex  anaemia. 

3.  Reflex  movements,  in  which  the  centripetal  impulse  passes  through  a 
sympathetic  nerve,  and    the  centrifugal  through  a  cerebro-spinal  nerve; 
most    of    these    phenomena    are    pathological,    e.  g.,    convulsions    from 
intestinal  irritation  produced  by  the  presence  of  worms,  eclampsia,  hysteria, 
etc. 

4.  Reflex  actions,  in  which  both  the  centripetal  and  centrifugal  impulses 
pass  through   filaments   of   the  sympathetic  nervous   system,  e.g.,  those 
obscure  reflex  actions  which  preside  over  the  secretions  of  the  intestinal 
fluids,  which  unite  the  phenomena  of  the  generative  organs,  the  dilatation 


124  HUMAN   PHYSIOLOGY. 

of  the  pupils  from  intestinal  irritation  (worms),  and   many  pathological 
phenomena. 

Laws  of  Reflex  Action.     (Pfluger.) 

1.  Law  of  Unilaterality.     If  a  feeble  irritation  be   applied  to  one  or 
more  sensory  nerves,  movement  takes  place  usually  on  one  side  only,  and 
that  upon  the  same  side  as  the  irritation. 

2.  Law  of  Symmetry.  If  the  irritation  becomes  sufficiently  intense,  motor 
reaction  is  manifested,  in  addition,  in  corresponding  muscles  of  the  opposite 
side  of  the  body. 

3.  Law  of  Intensity.     Reflex  movements  are  usually  more  intense  on  the 
side  of  the  irritation;  at  times  the  movements  of  the  opposite  side  equal 
them  in  intensity,  but  they  are  usually  less  pronounced. 

4.  Law  of  Radiation.     If  the  excitation  still  continues  to  increase,  it 
is  propagated  upward,  and  motor  reaction   takes  place  through  centrifugal 
nerves  coming  from  segments  of  the  cord  higher  up. 

5.  Law  of  Generalization.     When  the  irritation  becomes  very  intense,  it 
is  propagated  to  the  medulla  oblongata ;  motor  reaction  then  becomes  gen- 
eral, and  it  is  propagated  up  and  down  the  cord,  so  that   all  the  muscles  of 
the  body  are  thrown  into  action,  the  medulla  oblongata  acting  as  a  focus 
whence  radiate  all  reflex  movements. 

Special  Reflex  Movements. 

There  are  a  number  of  reflex  movements  taking  place  through  the  spinal 
cord,  a  study  of  which  enables  the  physician  to  determine  the  condition  of 
its  different  segments.  They  may  be  divided  into,  I.  Skin  or  superficial, 
and  2.  Tendon  or  deep  reflexes.  The  skin  reflexes  are  induced  by  irritation 
of  the  skin  and  mucous  membranes,  e.g.,  pricking,  pinching,  scratching,  etc. 
The  following  are  the  principal  skin  reflexes  : — 

1.  Plantar  reflex,  consisting  of  contraction  of  the  muscles  of  the  foot, 
induced  by  stimulation  of  the  sole  of  the  foot ;  it  involves  the  integrity  of 
the  reflex  arc  through  the  lower  end  of  the  cord. 

2.  Ghiteal  reflex,  consisting  of  contraction  of  the  glutei  muscles  when 
the  skin  over  the  buttock  is  stimulated ;  it  takes  place  through  the  segments 
giving  origin  to  the  fourth  and  fifth  lumbar  nerves. 

3.  Cremasteric  reflex,  consisting  of  a  contraction  of  the  cremaster  muscle, 
and  a  retraction  of  the  testicle  toward  the  abdominal  ring,  when  the  skin  on 
the  .inner  side  of  the  thigh  is  stimulated;  it  depends  upon  the  integrity  of 
the  segments  giving  origin  to  the  first  and  second  lumbar  nerves. 

4.  Abdominal  reflex,  consisting  of  a  contraction  of  the  abdominal  mus- 
cles when  the  skin  upon  the  side  of  the  abdomen  is  gently  scratched ;  its 


FUNCTIONS   OF  THE  SPINAL  CORD.  125 

production  requires  the  integrity  of  the  spinal  segments  from  the  eighth  to 
the  twelfth. 

5.  Epigastric  reflex,  consisting  of  a  slight  muscular  contraction  in  the 
neighborhood  of  the  epigastrium  when  the  skin  between  the  fourth  and  sixth 
ribs  is  stimulated ;  it  requires  the  integrity  of  the  cord  between  the  fourth 
and  seventh  dorsal  nerves. 

6.  Scapular   reflex  consists  of  a  contraction   of  the   scapular   muscles 
when  the  skin  between  the  scapula  is  stimulated;    it    depends  upon  the 
integrity  of  the  cord  between  the  fifth  cervical  and  third  dorsal  nerves. 

The  superficial  reflexes,  though  variable,  are  generally  present  in  health. 
They  are  increased  or  exaggerated  when  the  gray  matter  of  the  cord  is 
abnormally  excited,  as  in  tetanus,  strychnia  poisoning,  and  in  disease  of 
the  lateral  columns,  leading  to  arrest  of  their  normal  functions.  The  Ten- 
don or  deep  reflexes  are  also  of  great  value  in  diagnosing  the  condition  of 
the  spinal  segments.  They  are  induced  by  a  sharp  blow  upon  a  tendon. 
The  following  are  the  principal  forms : — 

1.  Patella  reflex  or  Knee  jerk,  consisting  of  a  contraction  of  the  extensor 
muscles  of  the  thigh  when  the  »ligamentum  patella  is  struck  between  the 
patella  and  tibia.     This  reflex  is  best  observed  when  the  legs  are  freely 
hanging  over  the  edge  of  a  table.     The  patella  reflex  is  generally  present  in 
health,  being  absent  in  only  2.  per  cent. ;  it  is  greatly  exaggerated  in  lateral 
sclerosis,  in  descending  degeneration  of  the  cord ;  it  is  absent  in  locomotor 
ataxia  and  in  atrophic  lesions  of  the  anterior  gray  cornuse. 

2.  Ankle  jerk  or  rejlex.     If  the  extensor  muscles  of  the  leg  be  placed 
upon  the  stretch  and  the  tendo-achillis  be  sharply  struck,  a  quick  extension 
of  the  foot  will  take  place. 

3.  Ankle  clonus.      This  consists  of  a  series  of  rhythmical  reflex  con- 
tractions of  the  gastrocnemius  muscle,  varying  in  frequency  from  6  to  10 
per  second.     To  elicit  this  reflex,  pressure  is  made  upon  the  sole  so  as  to 
suddenly  and  energetically  flex  the  foot  at  the  ankle,  thus  putting  the  tendo- 
achillis  upon  the  stretch.      The  rhythmical  movements  thus  produced  con- 
tinue so  long  as  the  tension  is  maintained.     Ankle  clonus  is  never  present 
in  health,  but  is  very  marked  in  lateral  sclerosis  of  the  cord. 

The  toe  reflex,  peroneal  reflex,  wrist  reflex  are  also  present  in  sclerosis  of 
the  lateral  columns  and  in  the  late  rigidity  of  hemiplegia. 

Special  Nerve  Centres  in  Spinal  Cord.  Throughout  the  spinal  cord 
there  are  a  number  of  special  nerve  centres,  capable  of  being  excited 
reflexly  and  producing  complex  coordinated  movements.  Though  for  the 
most  part  independent  in  action  they  are  subject  to  the  controlling  influences 
of  the  medulla  and  brain. 


126  HUMAN  PHYSIOLOGY. 

1.  Cilio-spinal  centre,  situated  in  the  cord  between  the  lower  cervical 
and  .third  dorsal  vertebra.     It  is  connected  with  the  dilatation  of  the  pupil 
through  fibres  which  emerge  in  this  region  and  enter  the  cervical  sympa- 
thetic.    Stimulation  of  the  cord  in  this  locality  causes  dilatation  of  the  pupil 
on  the  same  side ;  destruction  of  the  cord  is  followed  by  contraction  of  the 
pupil. 

2.  Genito-spinal  centre,  situated  in  the  lower  part  of  the  cord.     This  is 
a  complex  centre  and  comprises  a  series  of  subordinate  centres  for  the  con- 
trol of  the  muscular  movements  involved  in  the  acts  of  defecation,  micturi- 
tion, ejaculation  of  semen,  the  movements  of  the  uterus  during  parturition, 
etc. 

3.  Vasomotor  centres,  giving  origin  to   both  vaso-constrictor  and  vaso- 
dilator fibres,  which  are  distributed  throughout  the  cord.     Though  acting 
reflexly  they  are  under  the  dominating  influence  of  the  centre  in  the  me- 
dulla. 

4.  Sweat  centres  are  also  present  in  various  parts  of  the  cord. 
Paralysis  from  Injuries  of  the  Spinal  Cord. 

Seat  of  Lesion.  If  it  be  in  the  lower  phrt  of  the  sacral  canal,  there  is 
paralysis  of  the  compressor  urethrse,  accelerator  urinre,  and  sphincter  ani 
muscles ;  no  paralysis  of  the  muscles  of  the  leg. 

At  the  upper  limit  of  the  sacral  region.  Paralysis  of  the  muscles  of 
the  bladder,  rectum  and  anus ;  loss  of  sensation  and  motion  in  the  muscles 
of  the  legs,  except  those  supplied  by  the  anterior  crural  and  obturator, 
viz. :  psoas  iliacus,  Sartorius,  pectineus,  adductor  longus,  magnus  and 
brevis,  obturator,  vastus  externus  and  internus,  etc. 

At  the  upper  limit  of  the  lumbar  region.  Sensation  and  motion  para- 
lyzed in  both  legs;  loss  of  power  over  the  rectum  and  bladder;  paralysis 
of  the  muscular  walls  of  the  abdomen  interfering  with  expiratory  move- 
ments. 

At  the  lower  portion  of  the  cervical  region.  Paralysis  of  the  legs,  etc. 
as  above;  in  addition,  paralysis  of  all  the  intercostal  muscles  and  conse- 
quent interference  with  respiratory  movements ;  paralysis  of  muscles  of 
the  upper  extremities,  except  those  of  the  shoulders. 

Above  the  middle  of  the  cervical  region.  In  addition  to  the  preceding, 
difficulty  of  deglutition  and  vocalization,  contraction  of  the  pupils,  paralysis 
of  the  diaphragm,  scalene  muscles,  intercostals,  and  many  of  the  accessory 
respiratory  muscles ;  death  resulting  immediately,  from  arrest  of  respiratory 
movements. 


MEDULLA   OBLONGATA.  127 

MEDULLA  OBLONGATA. 

The  Medulla  Oblongata  is  the  expanded  portion  of  the  upper  part  of 
the  spinal  cord.  It  is  pyramidal  in  form  and  measures  one  and  a  half 
inches  in  length,  three-quarters  of  an  inch  in  breadth,  half  an  inch  in 
thickness,  and  is  divided  into  two  lateral  halves  by  the  anterior  and  pos- 
terior median  fissures,  which  are  continuous  with  those  of  the  cord.  Each 

FIG.  13. 


VIEW   OF   CEREBELLUM    IN   SECTION,   AND   OF   FOURTH    VENTRICLE,  WITH   THE 

NEIGHBORING  PARTS.    (From  Sappey.) 

i.  Median  groove  fourth  ventricle,  ending  below  in  the  calamus  scriptorius,  with  the 
longitudinal  eminences  formed  by  the  fasciculi  teretes,  one  on  each  side.  2.  The  same 
groove,  at  the  place  where  the  white  streaks  of  the  auditory  nerve  emerge  from  it  to 
cross  the  floor  of  the  ventricle.  3.  Inferior  peduncle  of  the  cerebellum,  formed  by  the 
restiform  body.  4.  Posterior  pyramid  :  above  this  is  the  calamus  scriptorius.  5.  Supe- 
rior peduncle  of  cerebellum,  or  processus  e  cerebello  ad  testes.  6  6.  Fillet  to  the  side 
of  the  crura  cerebri.  77.  Lateral  grooves  of  the  crura  cerebri.  8.  Corpora  quad- 
rigemina, — After  Hirschfeld  and  Leveille. 

half  is  again  subdivided  by  minor  grooves,  into  four  columns,  viz. :  anterior 
pyramid,  lateral  tract  and  olivary  body,  restiform  body  and  posterior 
pyramid. 

I.  The  anterior  pyramid  is  composed  partly  of  fibres  continuous  with 
those  of  the  anterior  column  of  the  spinal  cord;  but  mainly  of  fibres  de- 
rived from  the  lateral  tract  of  the  opposite  side,  by  decussation.  The 


128  HUMAN   PHYSIOLOGY. 

united  fibres  then  pass  upward  through  the  pons  Varolii  and  crura  cerebri, 
and  for  the  most  part  terminate  in  the  corpus  striatum  and  cerebrum. 

2.  The  lateral  tract  is  continuous  with  the  lateral  columns  of  the  cord ; 
its  fibres  in  passing  upward  take  three  directions,  viz. ;  an  external  bundle 
joins  the  restiform  body,  and  passes  into  the  cerebellum ;  an  internal  bundle 
decussates  at  the  median  line  and  joins  the   opposite  anterior  pyramid  ;  a 
middle  bundle  ascends  beneath  the  olivary  body,  behind  the  pons,  to  the 
cerebrum,  as  \\~\o.  fasciculus  teres. 

The  olivary  body  of  each  side  is  an  oval  mass,  situated  between  the 
anterior  pyramid  and  restiform  body ;  it  is  composed  of  white  matter  exter- 
nally and  gray  matter  internally,  forming  the  corpus  dentatum. 

3.  The  restiform  body,  continuous  with  the  posterior  column  of  the  cord, 
also  receives  fibres  from  the  lateral  column.     As  the  restiform  bodies  pass 
upward  they  diverge  and   form  a  space,  the  4th  ventricle,   the  floor  of 
which  is  formed  by  gray  matter,  and  then  turn  backward  and  enter  the 
cerebellum. 

4.  The  posterior  pyramid is  a  narrow,  white  cord  bordering  the  posterior 
median  fissure;  it  is  continued  upward,  in  connection  with  the  fasciculus 
teres ,  to  the  cerebrum. 

The  Gray  Matter  of  the  medulla  is  continuous  with  that  of  the  cord. 
It  is  arranged  with  much  less  regularity,  becoming  blended  with  the  white 
matter  of  the  different  columns,  with  the  exception  of  the  anterior.  By  the 
separation  of  the  posterior  columns,  the  transverse  commissure  is  exposed, 
forming  part  of  the  floor  of  the  4th  ventricle;  special  collections  of  gray 
matter  are  found  in  the  posterior  portions  of  the  medulla,  connected  with 
the  roots  of  origin  of  different  cranial  nerves. 

Properties  and  Functions.  The  medulla  is  excitable  anteriorly,  and 
sensitive  posteriorly  to  direct  irritation.  It  serves  (i)  as  a  conductor  of  sen- 
sitive impressions  upward  from  the  cord,  through  the  gray  matter  to  the 
cerebrum ;  (2)  as  a  conductor  of  voluntary  impulses  from  the  brain  to  the 
spinal  cord  and  ^nerves,  through  its  anterior  pyramids;  (3)  as  a  conductor 
of  coordinating  impulses  from  the  cerebellum,  through  the  restiform  bodies 
to  the  spinal  cord. 

As  an  Independent  Reflex  Centre.  The  medulla  oblongata  con- 
tains special  collections  of  gray  matter,  which  constitute  independent 
nerve  centres  which  preside  over  different  functions,  some  of  which  are  as 
follows,  viz.  : — 

I.  A  centre  which  controls  the  movements  of  mastication,  through 
afferent  and  efferent  nerves.  (See  page  25.) 


Motor 
or 


MEDULLA   OBLONGATA.  129 

2.  A  centre  reflecting  impressions  which  influence  the  secretion  of  saliva. 
(See  page  28.) 

3.  A  centre  for  sucking,  mastication  and  deglutition,  whence  are  derived 
motor  stimuli  exciting  to  action  and  coordinating  the  muscles  of  the  palate, 
pharynx  and  oesophagus,  necessary  for  the  swallowing  of  the  food.      The 
secretion  of  saliva  is  also  controlled  by  a  centre  in  the  medulla. 

NERVOUS  CIRCLE  OF  DEGLUTITION.     (2d  and  3d  Stages.) 

Excitor  ("     Palatal  branch  of  5th  pair. 

or  Pharyngeal  branches  of  the  glosso  pharyngeal. 

Centripetal  Superior  laryngeal  branches  of  the  pneumogastric. 

Nerves.  [     (Esophageal  branches  of  the  pneumogastric. 

Pharyngeal  branches  of  the  pneumogastric,  derived 

from  the  spinal  accessory. 

Hypoglossal  and  branches  of  the  cervical  plexus. 
Centrifugal  Inferior  or  recurrent  laryngeal. 

Nerves.  Motor  filaments  of  the  3d  division  of  the  5th  pair. 

Portio  dura. 

4.  A  centre  which  coordinates    the  muscles    concerned    in   the  act  ot 
vomiting. 

5.  A  Speech  centre,  coordinating  the  various  muscles  necessary  for  the 
accomplishment  of  articulation  through  the  hypoglossal,  facial  nerves  and 
the  2d  division  of  the  5th  pair. 

6.  A  centre  for  the  harmonization  of  muscles  concerned  in  expression, 
reflecting  its  impulses  through  the  facial  nerve. 

7.  A  Cardiac  centre,  which  exerts  (i)  an  accelerating  influence  over  the 
heart's  pulsations  through  accelerating  nerve  fibres  emerging  from  the  cer- 
vical portion  of  the  cord,  entering  the  inferior  cervical  ganglion,  and  thence 
passing  to  the  heart;  (2)  an  inhibitory  or  retarding  influence  upon  the  action 
of  the  heart,  through  fibres  of  the  spinal  accessory  nerve  running  in  the 
trunk  of  the  pneumogastric.     The  cardio-inhibitory  centre  is  in  a  state  of 
tonic  excitement   and  continuously  sending   impulses  to  the  heart  which 
exert  an  inhibitory  influence  upon  its  action.     It  may  be  stimulated  directly 
by  ancemia  as  well  as  venous  hyperaetniaof  the  blood  vessels  of  the  medulla 
and  increased  venosity  of  the  blood.     It  is  excited  reflexly  by  the  stimula- 
tion of  the  central  end  of  the  vagus,  sciatic  and  splanchnic  nerves. 

8.  A  Vasomotor  centre,  which   by  alternately  contracting   and  dilating 
the  blood  vessels  through  nerves  distributed  in  their  walls,  regulates  the 
quantity  of  blood  distributed  to  an  organ  or  tissue,  and  thus  influences 
nutrition,  secretion  and  calorification.     The  vasomotor  centre  is  situated  in 
the  medulla  oblongata  and  pons  Varolii,  between  the  corpora  quadrigemina 


130  HUMAN   PHYSIOLOGY. 

and  the  calamus  scriptorius.  The  vasomotor  fibres  having  their  origin  in 
this  centre  descend  through  the  interior  of  the  cord,  emerge  through  the 
anterior  roots  of  spinal  nerves,  enter  the  ganglia  of  the  sympathetic,  and 
thence  pass  to  the  walls  of  the  blood  vessels,  and  maintain  the  arterial 
tonus ;  they  may  be  divided  into  two  classes,  viz.;  vaso-dilators,  e.g., 
chorda  tympani,  and  vase-constrictors,  e.g.,  sympathetic  fibres. 

Division  of  the  cord  at  the  lower  border  of  the  medulla  is  followed  by  a 
dilatation  of  the  entire  vascular  system  and  a  marked  fall  of  the  blood  pres- 
sure. Galvanic  stimtdation  of  the  divided  surface  of  the  cord  is  followed 
by  a  contraction  of  the  blood  vessels  and  a  rise  in  the  blood  pressure. 

The  vasomotor  centre  is  stimulated  directly  by  the  condition  of  the 
blood  in  the  medulla  oblongata.  When  it  is  highly  venous  it  becomes  very 
active  and  the  blood  vessels  throughout  the  body  are  contracted  and  the 
blood  current  becomes  swifter;  sudden  anaemia  of  the  medulla  has  a  similar 
effect.  This  centre  may  be  increased  in  action  with  attendant  rise  of 
blood  pressure,  by  irritation  of  certain  afferent  nerve  fibres.  These  are 
known  as pressor  fibres.  On  the  other  hand,  its  action  may  be  depressed 
by  other  afferent  fibres  with  attendant  fall  of  blood  pressure.  These  are 
known  as  depressor  fibres. 

9.  A  Diabetic  centre,  irritation  of  which  causes  an  increase  in  the  amount 
of  urine  secreted,  and  the  appearance  of  a  considerable  quantity  of  sugar. 

10.  Respiratory  centre,  situated   near  the  origin  of  the  pneumogastric 
nerves,  presides  over  the  movements  of  respiration  and  its  modifications, 
laughing,  sighing,  sobbing,  sneezing,  etc.     It  may  be  excited  reflexly  by 
the  presence  of  carbonic  acid  in  the  lungs  irritating  the  terminal  pneumo- 
gastric filaments ;  or  automatically,  according  to  the  character  of  the  blood 
circulating  through  it ;  an  excess  of  carbonic  acid  or  a  diminution  of  oxygen 
increasing  the  number  of  respiratory  movements ;  a  reverse  condition  dimin- 
ishing the  respiratory  movements. 

11.  A  Spasm  centre,  stimulation  of  which  gives  rise  to  convulsive  phe- 
nomena, such  as  coughing,  sneezing,  etc. 

12.  A  centre  for  certain  ocular  functions,  governing  the  closure  of  the 
eyelids  and  dilatation  of  the  pupil. 

13.  A  Sweat  centre  is  also  localized  in  the  medulla. 

NERVOUS  CIRCLE  OF  RESPIRATION  (ENTIRELY  REFLEX), 
p,     .  f    Pulmonary  branches  of  the  pneumogastric. 

or  I     Superior  laryngeal. 

n     .  \    Trifacial,  or  5th  pair. 

Nerves  Nerves  of  &™^  sensibility- 

[    Sympathetic  nerve. 


CRURA  CEREBRI.  131 

-_  f  Phrenic,  distributed  to  the  diaphragm. 

|  Intercostals,  distributed  to  the  intercostal  muscles. 
r  °.rf  ,  -j  Facial  nerve,  or  portio  dura,  to  the  facial  muscles. 
Centntuga  External  branch  of  spinal  accessory,  to  the  trapezius 

erves.  an(j  sterno-cleido-mastoid  muscles. 


PONS  VAROLII. 

The  Pons  Varolii  unites  together  the  cerebrum  above,  the  cerebellum 
behind,  and  the  medulla  oblongata  below.  It  consists  of  transverse  and 
longitudinal  fibres,  amidst  which  are  irregularly  scattered  collections  of  gray 
or  vesicular  nervous  matter. 

The  transverse  fibres  unite  the  two  lateral  halves  of  the  cerebellum. 

The  longfaidinal  fibres  are  continuous  (i)  with  the  anterior  pyramids 
of  the  medulla  oblongata,  which  interlacing  with  the  deep  layers  of  the 
transverse  fibres,  ascend  to  the  crura  cerebri,  forming  their  superficial  or 
fasciculated  portions;  (2)  with  fibres  derived  from  the  olivary  fasciculus, 
some  of  which  pass  to  the  tubercula  quadrigemina,  while  others,  uniting 
with  fibres  from  the  lateral  and  posterior  columns  of  the  medulla,  ascend 
in  the  deep  or  posterior  portions  of  the  crura  cerebri. 

Properties  and  Functions.  The  superficial  portion  is  insensible  and 
inexcitable  to  direct  irritation ;  the  deeper  portion  appear  to  be  excitable, 
consisting  of  descending  motor  fibres ;  the  posterior  portions  are  sensible  but 
inexcitable  to  irritation. 

Transmits  motor  impulses  and  sensory  impressions  from  and  to  the 
cerebrum. 

The  gray  ganglionic  matter  consists  of  centres  which  convert  impressions 
into  conscious  sensations,  and  originate  motor  impulses,  these  taking  place 
independent  of  any  intellectual  process;  they  are  the  seat  of  instinctive 
reflex  acts;  the  centres  which  assist  in  the  coordination  of  the  automatic 
movements  of  station  and  progression. 


CRURA  CEREBRI. 

The  Crura  Cerebri  are  largely  composed  of  the  longitudinal  fibres  of 
the  pons  (anterior  pyramids,  fasciculi  teretes) ;  after  emerging  from  the  pons 
they  increase  in  size,  and  become  separated  into  two  portions  by  a  layer  of 
dark  gray  matter,  the  locus  niger. 

The  superficial  portion,  the  crusta,  composed  of  the  anterior  pyramids, 
constitute  the  motor  tract,  which  terminates,  for  the  most  part,  in  the  corpus 


132  HUMAN  PHYSIOLOGY. 

striatum,  but  to  some  extent,  also,  in  the  cerebrum;  the  deep  portion, 
made  up  of  the  fasciculi  teretes  and  posterior  pyramids  and  accessory  fibres 
from  the  cerebellum,  constitute  the  sensory  tract  (the  tegmentum\  which 
terminates  in  the  optic  thalamus  and  cerebrum. 

Function.  The  crura  are  conductors  of  motor  impulses  and  sensory 
impressions ;  the  gray  matter,  the  locus  niger,  assists  in  the  coordination  of 
the  complicated  movements  of  the  eyeball  and  iris,  through  the  motor  oculi 
communis  nerve.  They  also  assist  in  the  harmonization  of  general  muscular 
movements;  section  of  one  crus  giving  rise  to  peculiar  movements  of  rotation 
and  somersaults  forward  and  backward. 


CORPORA  QUADRIGEMINA. 

The  Corpora  Quadrigemina  are  four  small,  rounded  eminences,  two 
on  each  side  of  the  median  line,  situated  immediately  behind  the  third 
ventricle,  and  beneath  the  posterior  border  of  the  corpus  callosum. 

The  anterior  tubercles  are  oblong  from  before  backward,  and  larger  than 
the  posterior,  which  are  hemispherical  in  shape ;  they  are  grayish  in  color, 
but  consist  of  white  matter  externally  and  gray  matter  internally. 

Both  the  anterior  and  posterior  tubercles  are  connected  with  the  optic 
thalami  by  commissural  bands  named  the  anterior  and  posterior  brachia, 
respectively.  They  receive  fibres  from  the  olivary  fasciculus  and  fibres 
from  the  cerebellum,  which  pass  upward  to  enter  the  optic  thalami. 

The  corpora  geniculata  are  situated,  one  on  the  inner  side  and  one  on 
the  outer  side  of  each  optic  tract,  behind  and  beneath  the  optic  thalamus, 
and  from  their  position  are  named  the  corpora  genictilata  interna  and 
externa ;  they  give  origin  to  fibres  of  the  optic  nerve. 

Functions.  The  Tubercula  quadrigemina  are  the  physical  centres  of 
sight,  translating  the  luminous  impressions  into  visual  sensations.  Destruc- 
tion of  these  tubercles  is  immediately  followed  by  a  loss  of  the  sense  of 
sight;  moreover,  their  action  in  vision  is  crossed,  owing  to  the  decussation 
of  the  optic  tracts,  so  that  if  the  tubercle  of  the  right  side  be  destroyed  by 
disease  or  extirpated,  in  a  pigeon,  the  sight  is  lost  in  the  eye  of  the  oppo- 
site side,  and  the  iris  loses  its  mobility. 

The  tubercula  quadrigemina  as  nerve  centres  preside  over  the  reflex 
movements  which  cause  a  dilation  or  contraction  of  the  iris;  irritation  of 
the  tubercles  causing  contraction,  destruction  causing  dilatation.  Removal 
of  the  tubercles  on  one  side  produces  a  temporary  loss  of  power  of  the 
opposite  side  of  the  body,  and  a  tendency  to  move  around  an  axis  is  mani- 


CORPORA   STRIATA  AND   OPTIC  THALAMI.  133 

fested,  as  after  a  section  of  one  crus  cerebri,  which,  however,  may  be  due 
to  giddiness  and  loss  of  sight. 

They  also  assist  in  the  coordination  of  the  complex  movements  of  the 
eye,  and  regulate  the  movements  of  the  iris  during  the  movements  of 
accommodation  for  distance. 


CORPORA  STRIATA  AND  OPTIC  THALAMI. 

The  Corpora  Striata  are  two  large  ovoid  collections  of  gray  matter, 
situated  at  the  base  of  the  cerebrum,  the  larger  portions  of  which  are 
imbedded  in  the  white  matter,  the  smaller  portions  projecting  into  the 
anterior  part  of  the  lateral  ventricle.  Each  striated  body  is  divided,  by  a 
narrow  band  of  white  matter,  into  two  portions,  viz  : — 

1.  The  Caudate  nucleus,  the  intraventricular  portion,  which  is  conical 
in  shape,  having  its  apex  directed  backward,  as  a  narrow,  tail-like  process. 

2.  The  Lenticular  mtcleus,  imbedded  in  the  white  matter,  and  for  the 
most  part  external  to  the  ventricle;  on  the  outer  side  of  the   lenticular 
nucleus  is  found  a  narrow  band  of  white  matter,  the  external  capsule; 
and  between  it  and  the  convolutions  of  the  island  of  Reil,  a  thin  band  of 
gray  matter,  the  claustrum  ;  the  corpora  striata  are  grayish  in  color,  and 
when  divided  present  transverse  striations,  from  the  intermingling  of  white 
fibres  and  gray  cells. 

The  Optic  Thalami  are  two  oblong  masses  situated  in  the  ventricles 
posterior  to  the  corpora  striata,  and  resting  upon  the  posterior  portion  of 
the  crura  cerebri.  The  internal  surface  projecting  into  the  lateral  ven- 
tricles is  white,  but  the  interior  is  grayish,  from  a  commingling  of  both 
white  fibres  and  gray  cells.  Separating  the  lenticular  nucleus  from  the 
caudate  nucleus  and  the  optic  thalamus,  is  a  band  of  white  tissue,  the 
internal  capsule. 

The  internal  capsule  is  a  narrow,  bent  tract  of  white  matter,  and  is,  for 
the  most  part,  an  expansion  of  the  motor  tract  o/  the  crura  cerebri.  It 
consists  of  two  segments,  an  anterior,  situated  between  the  caudate 
nucleus  and  the  anterior  surface  of  the  lenticular  nucleus,  and  a  posterior, 
situated  between  the  optic  thalamus  and  the  posterior  surface  of  the  len- 
ticular nucleus.  These  two  segments  unite  at  an  obtuse  angle,  which  is 
directed  toward  the  median  line.  Pathological  observation  has  shown 
that  the  nerve  fibres  of  the  direct  and  crossed  pyramidal  tracts  can  be 
traced  upward  through  the  anterior  two-thirds  of  the  posterior  segment, 
into  the  centrum  ovale,  where,  for  the  most  part,  they  are  lost ;  a  portion, 


134  HUMAN  PHYSIOLOGY. 

however,  remaining  united,  ascend  higher  and  terminate  in  the  paracentral 
lobule,  the  superior  extremity  of  the  ascending  frontal  and  parietal  convo- 
lutions. The  sensory  tract  can  be  traced  upward,  through  the  posterior 
third,  into  the  cerebrum,  where  they  probably  terminate  in  the  hippo- 
campus major  and  unciate  convolution. 

Functions.  The  Corpora  striata  are  the  centres  in  which  terminate 
some  of  the  fibres  of  the  superficial  or  motor  tract  of  the  crura  cerebri ; 
others  pass  upward  through  the  internal  capsule,  to  be  distributed  to  the 
cerebrum.  It  might  be  inferred,  from  their  anatomical  relations,  that  they 
are  motor  centres.  Irritation  by  a  weak  galvanic  current  produces  mus- 
cular movements  of  the  opposite  side  of  the  body;  destruction  of  their 
substance  by  a  hemorrhage,  as  in  apoplexy,  is  followed  by  a  paralysis  of 
motion  of  the  opposite  side  of  the  body,  but  there  is  no  loss  of  sensation. 
When  the  hemorrhagic  destruction  involves  the  fibres  of  the  anterior  two- 
thirds  of  the  posterior  segment  of  the  internal  capsule,  and  thus  separates 
them  from  their  trophic  centres  in  the  cortical  motor  region,  a  descending 
degeneration  is  established,  which  involves  the  direct  pyramidal  tract  of 
the  same  side  and  the  crossed  pyramidal  tract  of  the  opposite  side. 

Destruction  of  the  posterior  one- third  of  the  posterior  segment  of  the 
internal  capsule  is  followed  by  a  loss  of  sensation  on  the  opposite  side  of  the 
body,  and  a  loss  of  the  senses  of  smell  and  vision  on  the  same  side  (Charcot). 
The  precise  function  of  the  corpora  striata  is  unknown,  but  they  are  in  some 
way  connected  with  motion. 

The  Optic  thalami  receives  the  fibres  of  the  tegmentum,  the  posterior 
portion  of  the  crura  cerebri.  They  are  insensible  and  inexcitable  to  direct 
irritation.  Removal  of  one  optic  thalamus,  or  destruction  of  its  substance 
by  disease  or  hemorrhage,  is  followed  by  a  loss  of  sensibility  of  the  opposite 
side  of  the  body,  but  there  is  no  loss  of  motion ;  their  precise  function  is 
also  unknown,  but  in  some  way  connected  with  sensation.  In  both  cases 
their  action  is  crossed. 


CEREBELLUM. 

The  Cerebellum  is  situated  in  the  inferior  fossae  of  the  occipital  bone, 
beneath  the  posterior  lobes  of  the  cerebrum.  It  attains  its  maximum 
weight,  which  is  about  5  ozs.,  between  the  twenty-fifth  and  fortieth  years  ; 
the  proportion  between  the  cerebellum  and  cerebrum  being  I  to  8£. 

It  is  composed  of  two  lateral  hemispheres  and  a  central  elongated  lobe, 
the  vermiform  process  ;  the  two  hemispheres  are  connected  with  each  other 
by  the  fibres  of  the  middle  peduncle  forming  the  superficial  portion  of  the 


CEREBELLUM.  135 

pons  Varolii.  It  is  brought  into  connection  with  the  medulla  oblongata 
and  spinal  cord,  through  the  prolongation  of  the  restiform  bodies ;  with 
the  cerebrum,  by  fibres  passing  upward  beneath  the  corpora  quadrigemina 
and  the  optic  thalami,  and  then  forming  part  of  the  diverging  cerebral 
fibres. 

Structure.  It  is  composed  of  both  white  and  gray  matter,  the  former 
being  internal,  the  latter  external,  and  convoluted,  for  economy  of  space. 

The  White  matter  consists  of  a  central  stem,  the  interior  of  which  is  a 
dentated  capsule  of  gray  matter,  the  corpus  denlatum.  From  the  external 
surface  of  the  stem  of  white  matter  processes  are  given  off,  forming  the 
lamince,  which  are  covered  with  gray  matter. 

The  Gray  matter  is  convoluted  and  covers  externally  the  laminated  pro- 
cesses; a  vertical  section  through  the  gray  matter  reveals  the  following 
structures : — 

1.  A  delicate  connective  tissue  layer,  just  beneath  the  pia  mater,  contain- 
ing rounded  corpuscles,  and  branching  fibres  passing  toward  the  external 
surface. 

2.  The  cells  of  Purkinje,  forming  a  layer  of  la-ge,  nucleated,  branched 
nerve  cells  sending  off  processes  to  the  external  layer. 

3.  A  granular  layer  of  small,  but  numerous  corpuscles. 

4.  Nerve  fibre  layer,  formed  by  a  portion  of  the  white  matter. 

Properties  and  Functions.  Irritation  of  the  cerebullum  is  not  followed 
by  any  evidences  either  of  pain  or  convulsive  movements ;  it  is,  therefore, 
insensible  and  inexcitable. 

Co-ordination  of  Movements.  Removal  of  the  superficial  portions 
of  the  cerebellum  in  pigeons  produces  feebleness  and  want  of  harmony  in 
the  muscular  movements;  as  successive  slices  are  removed,  the  movements 
become  more  irregular,  and  the  pigeon  becomes  restless ;  when  the  last 
portions  are  removed,  all  power  Q{  flying,  walking,  standing,  etc.,  is  entirely 
gone,  and  the  equilibrium  cannot  be  maintained,  the  power  of  coordinating 
muscular  movements  being  entirely  gone.  The  same  results  have  been 
obtained  by  operating  on  all  classes  of  animals. 

The  following  symptoms  were  noticed  by  Wagner,  after  removing  the 
whole  or  a  large  part  of  the  cerebellum.  I.  A  tendency  on  the  part  of  the 
animal  to  throw  itself  on  one  side,  and  to  extend  the  legs  as  far  as  possible. 
2.  Torsion  of  the  head  on  the  neck.  3.  Trembling  of  the  muscles  of  the 
body,  which  was  general.  4.  Vomiting  and  occasionally  liquid  evacua- 
tions. 

Forced  Movements.     Division  of  one  crus  cerebelli  causes  the  animal 


136  HUMAN   PHYSIOLOGY. 

to  fall  on  one  side  and  roll  rapidly  on  its  longitudinal  axis.  According  to 
Schiff,  if  the  peduncle  be  divided  from  behind,  the  animal  falls  on  the  same 
side  as  the  injury;  if  the  section  be  made  \r\front,  the  animal  turns  to  the 
opposite  side." 

Disease  of  the  cerebellum  partially  corroborates  the  result  of  -experi- 
ments ;  in  many  cases  symptoms  of  unsteadiness  of  gait,  from  a  want  of 
coordination,  have  been  noticed. 

Comparative  anatomy  reveals  a  remarkable  correspondence  between  the 
development  of  the  cerebellum  and  the  complexity  of  muscular  actions.  It 
attains  a  much  greater  development,  relatively  to  the  rest  of  the  brain,  in 
those  animals  whose  movements  are  very  complex  and  varied  in  character, 
such  as  the  kangaroo,  shark  and  swallow. 

The  cerebellum  may  possibly  exert  some  influence  over  the  sexual  func- 
tion, but  physiological  and  pathological  facts  are  opposed  to  the  idea  of  its 
being  the  seat  of  the  sexual  instinct.  It  appears  to  be  simply  a  centre  for 
the  coordination  and  equilibration  of  muscular  movements. 


CEREBRUM. 

The  Cerebrum  is  the  largest  portion  of  the  encephalic  mass,  constituting 
about  four-fifths  of  its  weight ;  the  average  weight  in  the  adult  male  is  from 
48  to  50  ozs.,  or  about  three  pounds,  while  in  the  adult  female  it  is  about 
five  ozs.  less.  After  the  age  of  forty  the  weight  of  the  cerebrum  gradually 
diminishes  at  the  rate  of  one  ounce  every  ten  years.  In  idiots  the  brain 
weight  is  often  below  the  normal,  at  times  not  amounting  to  more  than 
twenty  ounces. 

The  Blood  Supply  to  the  cerebrum  is  unusually  large,  considering  its 
comparative  bulk  ;  nearly  one-fifth  of  the  entire  volume  of  blood  being  dis- 
tributed to  it  by  the  carotid  and  vertebral  arteries.  These  vessels  anastomose 
so  freely,  and  are  so  arranged  within  the  cavity  of  the  cranium,  that  an 
obstruction  in  one  vessel  will  not  interfere  with  the  regular  supply  of  blood 
to  the  parts  to  which  its  branches  are  distributed.  A  diminished  amount,  or 
complete  cessation,  of  the  supply  of  blood  is  at  once  followed  by  a  sus- 
pension of  its  functional  activity. 

The  cerebrum  is  connected  with  the  pons  Varolii  and  medulla  oblongata 
through  the  crura  cerebri,  and  with  the  cerebellum,  through  the  superior 
peduncles.  It  is  divided  into  two  lateral  halves,  or  hemispheres,  by  the 
longitudinal  fissure  running  from  before  backward  in  the  median  line ;  each 
hemisphere  is  composed  of  both  white  and  gray  matter,  the  former  being 


CEREBRUM.  137 

internal,  the  latter  external ;  it  covers  the  surfaces  of  the  hemisphere  which 
are  infolded,  forming  convolutions,  for  economy  of  space. 

Fissures. 

1.  The  Fissure  of  Sylvius  is  one  of  the  most  important ;  it  is  the  first  to 
appear  in  the  development  of  the  foetal  brain,  being  visible  at  about  the 
third  month ;  in  the  adult  it  is  quite  deep  and  well  marked,  running  from 
the  under  surface  of  the  brain  upward,  outward  and  backward,  and  forms 
a  boundary  between  the  frojiial  and  temporo-sphenoidal  lobes. 

2.  The  Fissure  of  Rolando  is  second   in  importance,  and  runs  from  a 
point  on  the  convexity  near  the  median  line  transversely  outward  and  down- 
ward toward  the  fissure  of  Sylvius,  but  does  not  enter  it.     It  separates  the 
frontal  from  the  pajietal  lobe. 

3.  The  Parietal  fissure,  arising  a   short  distance  behind  the  fissure  of 
^  Rolando,  upon  the  convexity  of  the  hemisphere,  runs  downward  and  back- 
ward to  its  posterior  extremity. 

4.  The  Parieto-occipilal fissure  separating  the  occipital  from  the  parietal 
lobes.     Beginning  upon  the  outer  surface  of  the  cerebrum,  it  is  continued 
on  the  mesial  aspect  downward  and  forward  until  it  terminates  in  the  calca- 
rine  fissure. 

\  5.  The  Calloso-marginal  fissure  lying  upon  the  mesial  surface,  where  it 
runs  parallel  with  the  corpus  callosum. 

Secondary  fissures   of  importance   are   found  in  different   lobes  of  the 

^cerebrum,  separating  the  various  convolutions.  In  the  anterior  lobe 
are  found  the  pre-central,  superior  frontal  and  inferior  frontal  fissures  ; 
in  the  temporo-sphenoidal  lobes  are  found  the  first  and  second  temporo- 
sphenoidal  fissures  ;  in  the  occipital  lobe,  the  calca rine  and  hippo-campal 
fissures. 

Convolutions.     Frontal  lobe. 

The  Ascending  frontal  convolution,  situated  in  front  of  the  fissure  of 
-    Rolando,  runs  downward    and    forward  ;  it   is  continuous  above  with  the 
anterior  frontal,  and  below  with  the  inferior  frontal  convolution. 

The  Superior  frontal  convolution  is  bounded  internally  by  the  longitu- 
dinal fissure,  and  externally  by  the  superior  frontal  fissure;  it  is  connected 
with  the  superior  end  of  the  frontal  convolution,  and  runs  downward  and 
forward  to  the  anterior  extremity  of  the  frontal  lobe,  where  it  turns  back- 
ward, and  rests  upon  the  orbital  plate  of  the  frontal  bone. 

The  Middle  frontal  convolution,  the  largest  of  the  three,  runs  from  be- 
hind  forward,  along  the  sides  of  the  lobe,  to  its  anterior  part;  it  is  bounded 
above  by  the  superior  and  below  by  the  inferior  frontal  fissures. 
J 


138 


HUMAN    PHYSIOLOGY. 


The  Inferior  frontal  convolution  winds  around  the  ascending  branch  of 
the  fissure  of  Sylvius,  in  the  anterior  and  inferior  portion  of  the  cerebrum. 

Parietal  Lobe.  The  Ascending  parietal  convolution  is  situated  just 
behind  the  fissure  of  Rolando,  running  downward  and  forward;  above,  it 
becomes  continuous  with  the  upper  parietal  convolution,  and  below,  winds 
around  to  be  united  with  the  ascending  frontal. 

FIG. 14. 


DIAGRAM    SHOWING    FISSURES   AND    CONVOLUTIONS    OF   THE    LEFT   SIDE    OF    THE    HUMAN 

BRAIN. 

F,  frontal ;  P,  parietal ;  O,  occipital ;  T,  temporo-sphenoidal  lobe  ;  S,  fissure  of  Sylvius  ; 
S',  horizontal ;  S",  ascending  ramus  of  S  ;  c,  sulcus  centralis,  or  fissure  of  Rolando; 
A,  ascending  frontal,  and  B,  ascending  parietal,  convolution  ;  FI,  superior  ;  F2,  middle, 
and  F3,  inferior  frontal  convolutions ;  f1;  superior,  f2,  inferior,  frontal  fissures  ; 
fg.  sulcus  praecentralis  ;  P,  superior  parietal  lobule ;  P2,  inferior  parietal  lobule,  con- 
sisting of  p2,  supra-marginal  gyrus,  and  P'2,  angular  gyrus  ;  z"/,  sulcus  interparietalis  ; 
c  m,  termination  of  calloso-marginal  fissure;  Oj,  first,  O2,  second,  O3,  third,  occipital 
convolutions ;  p  <?,  parieto-occipital  fissure  ;  o,  transverse  occipital  fissure  ;  /?<>,  inferior 
longitudinal  occipital  fissure;  Tj,  first,  T2,  second,  T3,  temporo-sphenoidal,  convolu- 
tions,^, first,  /3,  second,  temporo-sphenoidal  fissures. — Landois'  Physiology. 


CEREBRUM.  139 

The  Upper  parietal  convolution  is  situated  between  the  parietal  and 
longitudinal  fissures. 

The  Supra- marginal  convolution  winds  around  the  superior  extremity 
of  the  fissure  of  Sylvius. 

The  Angular  convolution,  a  continuation  of  the  preceding,  follows  the 
parietal  fissure  to  its  posterior  extremity,  and  then  makes  a  sharp  angle 
downward  and  forward. 

Temporo-sphenoidal  Lobe.  Contains  three  well-marked  convolu- 
tions, the  superior,  middle  and  inferior,  separated  by  well-defined  fissures, 
and  continuous  posteriorly  with  the  convolutions  of  the  parietal  lobe. 

The  Occipital  Lobe  lies  behind  the  parieto-occipital  fissure,  and  con- 
tains the  superior,  middle  and  inferior  convolutions,  not  well  marked. 

The  Central  Lobe,  or  Island  of  Reil,  situated  at  the  bifurcation  of  the 
fissure  of  Sylvius,  is  a  triangular-shaped  cluster  of  six  convolutions,  the 
gyri  operti,  which  are  connected  with  those  of  the  frontal,  parietal,  and 
temporo-sphenoidal  lobes. 

Upon  the  inner  or  mesial  aspect  of  the  hemisphere  are  found  (Fig.  15) — 

1.  The  Par acentral  lobule,  lying  in  the  region  of  the  upper  extremity  of 
the  fissure  of  Rolando;  it  contains  the  large  giant  cells  of  Betz.     Injury  to 
this  convolution  is  followed  by  degeneration  of  the  motor  tract. 

2.  The    Gyrus  fornicatus,   lying   below   the    calloso-marginal   fissure. 
Running  parallel  with  the  corpus  callosum,  it  terminates  at  its  posterior 
border  in  the  hippocampal  gyms. 

3.  The  Gyrus  hippocampus  (H)  is  formed  by  the  union  of  the  preceding 
convolution  with  the  occipito-temporal.     It  runs  forward  and  terminates 
in  a  hooked  extremity — uncus. 

4.  The   Quadrate  lobule  or  precuneus  lies  between  the  upper  extremity 
of  the  calloso  marginal  fissure  and  the  parieto-occipital. 

5.  The  Cuneus  lies  posteriorly  to  the  quadrate  lobule.     It  is  a  wedge- 
shaped  mass  enclosed  by  the  calcarine  and  parieto-occipital  fissures. 

Structure.  The  Gray  matter  of  the  cerebrum,  about  one-eighth  of  an 
inch  thick,  is  composed  of  five  layers  of  nerve  cells  :  (i)  a  superficial  layer, 
containing  few  small  multipolar  ganglion  cells ;  (2)  small  ganglion  cells, 
pyramidal  in  shape;  (3)  a  layer  of  large  pyramidal  ganglion  cells  with 
processes  running  off  superiorly  and  laterally ;  (4)  the  granular  formation 
containing  nerve  cells;  (5)  spindle-shaped  and  branching  nerve  cells  of 
moderate  size. 

The  White  matter  consists  of  three  distinct  sets  of  fibres : — 

I.  The  diverging  or  peduncular  fibres   are  mainly   derived   from   the 


140 


HUMAN   PHYSIOLOGY. 


columns  of  the  cord  and  medulla  oblongata ;  passing  upward  through  the 
crura  cerebri,  they  receive  accessory  fibres  from  the  olivary  fasciculus,  cor- 
pora quadrigemina  and  cerebellum.  Some  of  the  fibres  terminate  in  the 
optic  thalami  and  corpora  striata,  while  others  radiate  into  the  anterior 
middle  and  posterior  lobes  of  the  cerebrum. 

2.  The  transverse   commissural  fibres  connect  together  the  two  hemi- 
spheres, through  the  corpus  callosum  and  anterior  and  posterior  commis- 
sures. 

3.  The  longitudinal  commissural  fibres  connect  together  different  parts 
of  the  same  hemisphere. 

FIG.  15. 

*     c     B 


po 


DIAGRAM    SHOWING    FISSURES   AND   CONVOLUTIONS   ON   MESIAL   ASPECT   OF   THE    RIGHT 
HEMISPHERE. 

Median  aspect  of  the  right  hemisphere.  CC,  corpus  callosum  divided  longitudinally  : 
Gf,  gyrus  fornicatus ;  H,  gyms  hippocampi;  h,  sulcus  hippocampi;  TJ,  uncinate 
gyms  ;  cm,  calloso-marginal  fissure  ;  F,  first  frontal  convolution  ;  c,  terminal  portion 
of  fissure  of  Rolando ;  A,  ascending  frontal ;  B,  ascending  parietal  convolution  and 
paracentral  lobule;  PI',  praecuneus  or  quadrate  lobule;  Oz,  cuneus ;  Po,  parieto- 
occipital  fissure;  o\,  transverse  occipital  fissure;  oc,  calcarine  fissure;  oc' ,  superior, 
oc" ,  inferior  ramus  of  the  same  ;  D,  gyrus  descendens ;  T4,  gyrus  occipito-temporalis 
lateralis  (lobulus  fusiformis) ;  T5,  gyrus  occipito-temporalis  medialis  (lobulus  lin- 
gualis). 

Functions.  The  cerebral  hemispheres  are  the  centres  of  the  nervous 
system  through  which  are  manifested  all  the  phenomena  of  the  mind; 
they  are  the  centres  in  which  impressions  are  registered,  and  reproduced 
subsequently  as  ideas ;  they  are  the  seat  of  intelligence,  reason  and  will. 


FIG.  16. 


SIDE  VIEW  OF  THH  BRAIN  OF   MAN,  WITH  THE  AREAS  OF  THE  CEREBRAL  CONVOLUTIONS, 
ACCORDING  TO  FERRIER. 

The  figures  are  constructed  by  marking  on  the  brain  of  man,  in  their  respective 
situations,  the  areas  of  the  brain  of  the  monkey  as  determined  by  experiment,  and 
the  description  of  the  effects  of  stimulating  the  various  areas  refers  to  the  brain  of 
the  monkey. 

(i)  Advance  of  the  opposite  hind  limb,  as  in  walking. 
(2).  (3),  (4)  Complex  movements  of  the  opposite  leg  and  arm,  and  of  the  trunk,  as  in 

swimming. 
(a),  (b),  (c),  (d)  Individual  and  combined  movements  of  the  fingers  and  wrist  of  the 

opposite  hand.     Prehensile  movements. 

(5)  Extension  forward  of  the  opposite  arm  and  hand. 

(6)  Supination  and  flexion  of  the  opposite  forearm. 

(7)  Retraction  and  elevation  of  the  opposite  angle  of  the  mouth,  by  means  of  the  zygo- 
matic  muscles. 

(8)  Elevation  of  the  ala  nasi  and  upper  lip,  with  depression  of  the  lower  lip  on  the  oppo- 
site side. 

(9),  (10)  Opening  of  the  mouth,  with  (9)  protrusion  and  (10)  retraction  of  the  tongue; 

region  of  aphasia,  bilateral  action. 

(n)  Retraction  of  the  opposite  angle  of  the  mouth,  the  head  turned  slightly  to  one  side. 
(12)  The  eyes  open  widely,  the  pupils  dilate  and  the  head  and  eyes  turn  toward  the 

opposite  side. 
(13),  (13')  The  eyes  move  toward  the  opposite  side  with  an  upward  (13)  or  downward 

(13')  deviation.     The  pupils  are  generally  contracted. 
(14)  Pricking  of  the  opposite  ear,  the  head  and  eyes  turn  to  the  opposite  side,  and  the 

pupils  dilate  largely. 

141 


142  HUMAN   PHYSIOLOGY. 

However  important  a  centre  the  cerebrum  may  be,  for  the  exhibition  of 
this  highest  form  of  nervous  action,  it  is  not  directly  essential  for  the  con- 
tinuance of  life;  for  it  does  not  exert  any  control  over  those  automatic 
reflex  acts,  such  as  respiration,  circulation,  etc.,  which  regulate  the  functions 
of  organic  life. 

From  the  study  of  comparative  anatomy,  pathology,  vivisection,  etc., 
evidence  has  been  obtained  which  throws  some  light  upon  the  physiology 
of  the  cerebral  hemispheres. 

1.  Comparative  Anatomy  shows  that  there  is  a  general  connection  be- 
tween the  size  of  the  brain,  its  texture,  the  depth  and  number  of  convolu- 
tions, and  the  exhibition  of  mental  power.     Throughout  the  entire  animal 
series,  the  increase  in  intelligence  goes  hand  in  hand  with  an  increase  in 
the  development  of  the  brain.     In  man  there  is  an  enormous  increase  in 
size  over  that  of  the  highest  animals,  the  anthropoids.     The  most  cultivated 
races  of  men  have  the  greatest   cranial  capacity;    that  of  the   educated 
European  being  about  116  cubic  inches,  that  of  the  Australian  being  about 
60  cubic  inches,  a  difference  of  56  cubic  inches.     Men  distinguished  for 
great  mental  power  usually  have  large  and  well-developed  brains ;  that  of 
Cuvier  weighed  64  ozs. ;  that  of  Abercrombie  63  ozs. ;  the  average  being 
about  48  to  50  ozs. ;    not  only  the  size,  but  above  all,  the  texture  of  the 
brain,  must  be  taken  into  consideration. 

2.  Pathology.     Any  severe   injury  or   disease   disorganizing  the  hemi- 
spheres is  at  once  attended  by  a  disturbance,  or  entire  suspension  of  mental 
activity.     A  blow  on  the  head  producing  concussion,  or  undue  pressure 
from  cerebral  hemorrhage  destroys  consciousness;   physical  and  chemical 
alterations  in  the  gray  matter  have  been  shown  to  coexist  with  insanity 
loss  of  memory,  speech,  etc.     Congenital  defects  of  organization  from  im- 
perfect development  are  usually  accompanied  by  a  corresponding  deficiency 
of  intellectual  power  and  the  higher  instincts.     Under  these  circumstances 
no  great  advance  in  mental  development  can  be  possible,  and  the  intelli- 
gence remains  at  a  low  grade.     In  congenital  idiocy  not  only  is  the  brain 
of  small  size,  but  it  is  wanting  in  proper  chemical  composition;  phosphorus, 
a  characteristic  ingredient  of  the  nervous  tissue,  being  largely  diminished 
in  amount. 

3.  Experimentation  upon  the  lower  animals  by  removing  the  cerebral 
hemispheres  is  attended  by  results  similar  to  those  observed  in  disease  and 
injury.     Removal  of  the  cerebrum  in  pigeons  produces  complete  abolition 
of  intelligence,  and  destroys  the  capability  of  performing  spontaneous  move- 
ments.    The  pigeon  remains  in  a  condition  of  profound  stupor,  which  is 
not  accompanied,  however,  by  a  loss  of  sensation,  or  of  the  power  of  pro- 


CEREBRAL  LOCALIZATION   OF   FUNCTION.  143 

ducing  reflex  or  instinctive  movements.  The  pigeon  can  be  temporarily 
aroused  by  pinching  the  feet,  loud  noises,  light  placed  before  the  eyes,  etc., 
but  soon  relapses  into  a  state  of  quietude,  being  unable  to  remember  im- 
pressions and  connect  them  with  any  train  of  ideas ;  the  faculties  of 
memory,  reason  and  judgment  being  completely  abolished. 


CEREBRAL  LOCALIZATION  OF  FUNCTION. 

From  experiments  made  upon  animals,  and  the  results  of  clinical  and  post- 
mortem observations  upon  men,  it  has  been  shown  that  the  phenomena  of 
organic  and  psychical  life  are  presided  over  by  anatomically  localized  centres 
in  the  brain.  A  knowledge  of  the  position  of  these  centres  becomes  of  the 
highest  importance  in  localizing  the  seat  of  lesions,  thrombi,  hemorrhages, 
new  growths,  etc.,  which  show  themselves  in  paralysis,  epilepsies,  etc. 
It  has  not  been  possible  to  thus  localize  all  functions,  and  to  many  parts  of 
the  brain  no  special  use  can  be  assigned.  The  following  are  the  centres 
most  definitely  mapped  out  and  that  are  of  paramount  importance : — 

Motor  Centres.  These  are  in  the  cortical  gray  matter,  and  are  arranged 
along  either  side  of  the  fissure  of  Rolando.  This  area  is  known  as  the 
motor  area  or  motor  zone,  stimulation  of  which  is  followed  by  convulsive 
movements  of  the  muscles  of  the  opposite  side  of  the  body,  while  destruc- 
tion of  the  gray  matter  of  this  area  is  followed  by  permanent  paralysis  of 
the  muscles  of  the  opposite  side.  From  experiments  made  upon  monkeys, 
Ferrier  has  mapped  out  a  number  of  motor  centres  which  he  has  transferred 
to  corresponding  localities  on  the  human  brain  (see  Fig.  16).  The  descrip- 
tive test  of  the  figure  renders  his  results  intelligible.  Pathological  studies 
have  largely  confirmed  his  deductions.  In  a  general  way  it  may  be  said 
that  the  upper  third  of  the  ascending  frontal  and  parietal  convolutions 
about  this  fissure  preside  over  the  movements  of  the  leg  of  the  opposite  side 
of  the  body;  the  middle  third  controls  the  movements  of  the  arm;  the 
upper  part  of  the  inferior  third  is  the  facial  area.  The  lowest  part  of  the 
inferior  third  governs  the  motility  of  the  lips  and  tongue,  and  this  space, 
with  the  posterior  extremity  of  the  third  frontal  convolution,  constitutes  the 
speech  centre. 

The  experiments  of  Horsley  and  Schafer  have  enabled  them  to  furnish 
a  new  diagrammatic  representation  of  the  motor  area  and  to  more  accurately 
define  the  special  areas  upon  the  lateral  and  mesial  aspects  of  the  brain  of 
the  monkey.  The  boundaries  of  the  general  and  special  areas  as  deter- 


144  HUMAN   PHYSIOLOGY. 

mined  by  these  observers  will  be  readily  understood  by  an  examination  of 
Figures  17  and  18. 

For  diagnostic  purposes  the  motor  areas  for  the  face  and  limbs  have  been 
subdivided  as  follows  : — 

1.  The  face  area  may  be  divided  into  an  upper  part  comprising  about 
one-third,  and  a  lower  part  comprising  the  remaining  two-thirds.     In  the 
upper  part  are  centres  governing  the  movements  of  the  muscles  of  the  oppo- 
site angle  of  the  mouth  and  of  the  lower  face.     The  anterior  portion  of  the 
lower  two-thirds  controls  the  movements  of  the  vocal   cords  and  may  be 
regarded  as  a  laryngeal  centre;  the  posterior  portion  governs  the  opening 
and  shutting  of  the  mouth  and  the  protrusion  and  retraction  of  the  tongue. 

2.  The  upper  limb  area  may  be  subdivided  as  follows  :  The  upper  part 

FIG.  17. 


DIAGRAM    OF   THE    MOTOR    AREAS    ON    THE    OUTER    SURFACE    OF    A    MONKEY  S    BRAIN. 

Horsley  and  Schafer. 

controls  the  movements  of  the  shoulder;  posterior  and  below  this  point  are 
centres  for  the  elbow ;  below  and  anteriorly,  centres  for  the  wrist  and  finger 
movements,  while  lowest  and  posteriorly  centres  governing  the  thumb. 

3.  The  leg  area  may  be  subdivided  as  follows  :  The  anterior  part,  both 
on  the  mesial  and  lateral  surfaces,  contains  centres  governing  the  hip  and 
thigh  movements;  in  the  posterior  part  are  centres  for  the  movements  of 
the  leg  and  toes.     The  centre  for  the  big  toe  has  been  located  in  the  para- 
central  lobule. 

4.  The  trunk  area,  situated    largely  on    the    mesial    surface,  contains 
anteriorly  centres  governing  the  rotation  and  arching  of  the  spine,  while 
posteriorly  are  found  centres  governing  movements  of  the  tail  and  pelvis. 

5.  The  head  area,  or  area  for  visual  direction,  contains  centres,  excita- 


CEREBRAL    LOCALIZATION   OF    FUNCTION.  145 

tion  of  which  causes  "  opening  of  the  eyes,  dilatation  of  the  pupils  and 
turning  of  the  head  to  the  opposite  side  with  conjugate  deviation  of  the 
eyes  to  that  side." 

The  centres  of  origin  of  the  nerves  for  the  ocular  muscles  lie  in 
the  gray  matter  of  the  aqueduct  of  Sylvius.  Destruction  of  the  gray 
matter  at  these  points  is  followed  by  paralysis  of  the  muscles  of  the 
opposite  side  of  the  body,  and  morbid  growths,  hemorrhages  or  thrombi  of 
the  vessels  of  the  parts,  result  in  abnormal  stimulation  or  interference  of  the 
functions  corresponding  to  the  nature  and  extent  of  the  lesion.  Cerebral  or 
Jacksonian  epilepsy  is  a  result  of  local  cortical  disease. 

Centre  for  Speech.  Pathological  investigations  have  demonstrated 
that  the  left  third  frontal  convolution  is  of  essential  importance  for  speech. 

FIG. 18. 


DIAGRAM    OF   THE    MOTOR    AREAS    ON   THE    MARGINAL    CONVOLUTION    OF    A    MONKEY'S 

BRAIN. — Horsley  and  Schafer. 

Adjoining  this  convolution  are  the  centres  controlling  the  motility  of  the 
lips,  tongue,  etc.  In  the  majority  of  the  cases  the  speech  centres  are  on  the 
left  side  of  the  brain,  though  in  exceptional  cases  it  is  on  the  right  side, 
especially  in  left-handed  people.  In  deaf-mutes  this  convolution  is  very 
imperfectly  developed,  while  in  monkeys  it  is  quite  rudimentary. 

Lesions  of  the  third  frontal  convolution  on  the  left  side,  if  the  patient  be 
right-handed,  produce  the  various  forms  of  aphasia  or  the  partial  or  com- 
plete loss  of  the  power  of  articulate  speech. 

Aphasia  is  of  many  degrees  and  kinds.  In  ataxic  aphasia  the  patient  is 
unable  to  communicate  his  thoughts  by  words,  there  being  an  inability  to 
execute  the  movements  of  the  mouth,  etc.,  necessary  for  speech.  In 


146 


HUMAN   PHYSIOLOGY. 


FIG.  19. 


agraphic  aphasia  there  is  an  inability  to  execute  the  movements  necessary 
for  writing,  though  the  mental  processes  are  retained.  In  the  ataxic  form 
the  lesion  is  in  the  3d  frontal  convolution,  and  in  the  agraphic  form  it  is  in 
the  arm  centre. 

In  Amnesic  Aphasia  there  is  a  loss  of  the  memory  of  words,  the  purest 
examples  of  which  consist  of  the  affections  known  as  word  deafness  and 
word  blindness.  In  word  deafness  the  patient  cannot  understand  vocal 
speech,  though  he  is  capable  of  hearing  other  sounds.  This  condition  is 
associated  with  lesion  of  the  first  temporal  convolution.  In  word  blindness 

the  patient  cannot  name  a 
letter  or  a  word  when 
printed  or  written,  though 
he  can  see  all  other  objects. 
This  condition  is  associated 
with  impairment  of  the  visual 
centres. 

Figure  19  will  illustrate 
the  conditions  in  the  various 
forms  of  aphasia.  Impres- 
sions are  constantly  passing 
from  eye  and  ear  to  the 
visual  and  auditory  centres 
and  there  registered.  Com- 
missural  fibres  connect  these 
centres  with  the  arm  and 
speech  centres,  which  in  turn 
are  connected  by  efferent 
fibres  with  the  muscles  of 
the  hand  and  vocal  appa- 
ratus. Muscular  movements 
of  the  eyes,  hand  and  mouth 
are  also  registered  by  means 
of  the  afferent  fibres  s,  s',  s". 
Sensory  Centres.  These 
are  the  centres  in  which  the 
sensory  impressions  are  co- 
ordinated, and  in  which  they 
probably  become  parts  of  our  consciousness.  The  most  important  are  : — 

The  Visual  Centre,  located  in  the  occipital  lobe  and  especially  in  the 
cuneus.  Unilateral  destruction  of  this  area  results  in  hemianopsia,  or 


SYMPATHETIC   NERVOUS   SYSTEM.  147 

blindness  of  the  corresponding  halves  of  the  two  retinae.  Destruction  of 
both  occipital  lobes  in  man  results  in  total  blindness.  Stimulation  or  irri- 
tation of  the  visual  centre  causes  photopsia,  or  hallucinations  of  sight,  in 
corresponding  halves  of  the  retinae.  There  have  been  instances  of  injury  of 
these  parts  when  sensations  of  color  were  abolished  with  preservation  of 
those  of  space  and  light,  thus  showing  a  special  localization  of  the  color 
centre.  Late  experiments  show  that  the  centres  of  the  two  hemispheres  are 
united,  as  ocular  fatigue  of  a  non-used  eye  was  proportional  to  the  fatigue 
of  the  exercised  one. 

The  Auditory  Centres  are  located  in  the  temporo-sphenoidal  lobes. 
Word  deafness  is  associated  with  softening  of  these  parts,  and  their  complete 
removal  results  in  deafness. 

The  Gustatory  and  Olfactory  Centres  are  located  in  the  uncinate  gyrus, 
on  the  inner  side  of  the  temporo-sphenoidal  lobes.  There  does  not  seem  to 
be  any  differentiation,  up  to  this  time,  of  these  two  centres. 

The  centre  for  tactile  impressions  was  located  by  Ferrier  in  the  hippo- 
campal  region.  Horsley  and  Schafer  found  that  destructive  lesions  of  the 
gyrus  fornicatus  was  followed  by  hemianaesthesia  of  the  opposite  side  of  the 
body,  which  was  more  or  less  marked  and  persistent.  These  observers 
conclude  that  the  limbic  lobe  "  is  largely,  if  not  exclusively,  concerned  in  the 
appreciation  of  sensations  painful  and  tactile." 

The  Superior  and  Middle  Frontal  convolutions  appear  to  be  the  seat  of 
the  reason,  intelligence  and  will.  Destruction  of  these  parts  is  fol- 
lowed by  proportional  hebetude,  without  any  impairment  of  sensation  or 
motion. 


SYMPATHETIC    NERVOUS  SYSTEM. 

The  Sympathetic  Nervous  System  consists  of  a  chain  of  ganglia 
connected  together  by  longitudinal  nerve  filaments,  situated  on  each  side  of 
the  spinal  column,  running  from  above  downward.  The  two  ganglionic 
cords  are  connected  together  in  the  interior  of  the  cranium  by  the  ganglion 
of  Ribes,  on  the  anterior  communicating  artery,  and  terminate  in  the  gan- 
glion impar,  situated  at  the  top  of  the  coccyx. 

The  chain  of  ganglia  is  divided  into  groups,  and  named  according  to  the 
location  in  which  they  are  found,  viz.:  cranial,  four  in  number  ;  cervical, 
three;  thoracic,  twelve ;  lumbar,  five;  sacral,  five;  coccygeal,  one.  Each 
ganglion  consists  of  a  collection  of  vesicular  nervous  matter,  bundles  of 
non-medullated  nerve  fibres,  imbedded  in  a  capsule  of  connective  tissue. 


148  HUMAN   PHYSIOLOGY. 

The  ganglia  are  reinforced  by  motor  and  sensory  fibres  from  the  cerebro- 
spinal  nervous  system. 

The  Ganglia  have  distinct  nerve  fibres  from  which  branches  are  dis- 
tributed to  the  glands,  arteries,  muscles,  and  to  the  cerebral  and  spinal 
nerves;  many  pass,  also,  to  the  visceral  ganglia,  e.g.,  cardiac,  semilunar, 
pelvic,  etc. 

Cephalic  Ganglia. 

1.  The   Ophthalmic  or  Ciliary  ganglion  is  situated  in  the  orbital  cavity 
posterior  to  the  eyeball ;  it  is  of  small  size,  and  of  a  reddish-gray  color ; 
receives  filaments  of  communication  from  the  motor  oculi,  ophthalmic  branch 
of  the  5th  pair,  and  the  carotid  plexus.    Its  filaments  of  distribution  are  the 
ciliary  nerves,  which  consist  of — 

1.  Motor  fibres  for  the  circular  fibres  of  the  iris  and  ciliary  muscle. 

2.  Sensory  fibres  for  the  cornea,  iris  and  associated  parts. 

3.  Vasomotor  fibres  for    the   blood  vessels  of  the  choroid,  iris  and 
retina. 

4.  Motor  fibres  for  the  dilator  fibres  of  the  iris. 

2.  The  Spheno-palatine,  or  Meckel's  ganglion,  triangular   in   shape,  is 
situated  in  the  spheno-maxillary  fossa ;    receives  filaments  from  the  facial 
(Vidian  nerve),  and  the  superior  maxillary  branch  of  the  5th  nerve     Its 
filaments  of  distribution  pass  to  the  gums,  the  soft  palate,  levator  palati  and 
azygos  uvulae  muscles. 

3.  The  Otic,  or  Arnold's  ganglion,  is  of  small  size,  oval  in  shape,  and 
situated  beneath  the  foramen  ovale ;  receives  a  motor  filament  from  the 
facial  and   sensory  filaments   from  the  glosso-pharyngeal  and  5th  nerve; 
sends  filaments  to  the  mucous  membrane  of  the  tympanic  cavity  and  to  the 
tensor  tympani  muscle. 

4.  The    Submaxillary  ganglion,    situated   in     the    submaxillary  gland, 
receives  filaments  from  the  chorda  tympani,  sensory  filaments  from  the  lin- 
gual branch  of  the  5th  nerve,  and  filaments  from  the  sympathetic.     The 
chorda  tympani  nerve  supplies  vaso-dilator  and  secretory  fibres  to  the  sub- 
maxillary and  sub-lingual  glands.     The  fifth  nerve  endows  the  glands  with 
sensibility,  while  the  sympathetic  supplies  secretory  or  trophic  fibres. 

Cervical  Ganglia. 

The  Superior  cervical  ganglion  is  fusiform  in  shape,  of  a  grayish-red 
color,  and  situate  opposite  the  2d  and  3d  cervical  vertebrae;  it  sends 
branches  to  form  the  carotid  and  cavernous  plexuses  which  follow  the 
course  of  the  carotid  arteries  to  their  distribution ;  also  sends  branches  to 


SYMPATHETIC   NERVOUS   SYSTEM.  149 

join  the  glosso-pharyngeal  and  pneumogastric,  to  form  the  pharyngeal 
plexus. 

The  Middle  cervical  ganglion,  the  smallest  of  the  three,  is  occasionally 
wanting;  it  is  situated  opposite  the  5th  cervical  vertebra;  sends  branches 
to  the  superior  and  inferior  cervical  ganglion,  and  to  the  thyroid  artery. 

The  Inferior  cervical  ganglion,  irregular  in  form,  is  situated  opposite  the 
last  cervical  vertebra ;  it  is  frequently  fused  with  the  first  thoracic  ganglion. 

The  superior,  middle  and  inferior  cardiac  nerves,  arising  from  these 
cervical  ganglia,  pass  downward  and  forward  to  form  the  deep  and  super- 
ficial cardiac  plexuses  located  at  the  bifurcation  of  the  trachea,  from  which 
branches  are  distributed  to  the  heart,  coronary  arteries,  etc. 

The  Thoracic  Ganglia  are  usually  twelve  in  number,  placed  against 
the  heads  of  the  ribs  behind  the  pleura ;  they  are  small  in  size  and  gray  in 
color;  they  communicate  with  the  cerebro  spinal  nerves  by  two  filaments, 
one  of  which  is  white,  the  other  gray. 

The  great  splanchnic  nerve  is  formed  by  the  union  of  branches  from  the 
sixth,  seventh,  eighth  and  ninth  ganglia ;  it  passes  through  the  diaphragm 
to  the  semilunar  ganglion. 

The  lesser  splanchnic  nerve  is  formed  by  the  union  of  filaments  from  the 
tenth  and  eleventh  ganglia,  and  is  distributed  to  the  cceliac  plexus. 

The  renal  splanchnic  nerve  arises  from  the  last  thoracic  ganglion  and 
terminates  in  the  renal  plexus. 

The  semilunar  ganglia,  the  largest  of  the  sympathetic,  are  situated  by 
the  side  of  the  coeliac  axis;  they  send  radiating  branches  to  form  the  solar 
plexus;  from  the  various  plexuses,  nerves  follow  the  gastric,  splenic, 
hepatic,  renal,  etc.,  arteries,  into  the  different  abdominal  viscera. 

The  Lumbar  Ganglia,  four  in  number,  are  placed  upon  the  bodies  of 
the  vertebrae;  they  give  off  branches  which  unite  to  form  the  aortic  lumbar 
plexus  and  the  hypogastric  plexus,  and  follow  the  blood  vessels  to  their 
terminations. 

The  Sacral  and  Coccygeal  Ganglia  send  filaments  of  distribution  to 
all  the  blood  vessels  of  the  pelvic  viscera. 

Properties  and  Functions.  The  sympathetic  nerve  possesses  both 
sensibility  and  the  power  of  exciting  motion,  but  these  properties  are  much 
less  decided  than  in  the  cerebro -spinal  system.  Irritation  of  the  ganglia 
does  not  produce  any  evidence  of  pain  until  some  time  has  elapsed.  If 
caustic  soda  be  applied  to  the  semilunar  ganglia,  or  a  galvanic  current  be 
passed  through  the  splanchnic  nerves,  no  instantaneous  effect  is  noticed,  as 
in  the  case  of  the  cerebro-spinal  nerves ;  but  in  the  course  of  a  few  seconds 


150  HUMAN   PHYSIOLOGY. 

a  slow,  progressive  contraction  of  the  muscular  coat  of  the  intestines  is 
established,  which  continues  for  some  time  after  the  irritation  is  removed. 
Division  of  the  sympathetic  nerve  in  the  neck  is  followed  by  a  vascular 
congestion  of  the  parts  above  the  section  on  the  corresponding  side,  attended 
by  an  increase  in  the  temperature ;  not  only  is  there  an  increase  in  the 
amount  of  blood,  but  the  rapidity  of  the  blood  current  is  very  much  hastened, 
and  the  blood  in  the  veins  becomes  of  a  brighter  color.  Galvanization  ot 
the  upper  end  of  the  divided  nerve  causes  all  of  the  preceding  phenomena 
to  disappear;  the  congestion  decreases,  the  temperature  falls,  and  the  venous 
blood  becomes  dark  again. 

The  sympathetic  exerts  a  similar  influence  upon  the  circulation  of  the 
limbs  and  the  glandular  organs ;  destruction  of  the  first  thoracic  ganglion 
and  division  of  the  nerves  forming  the  lumbar  and  sacral  plexuses,  is  fol- 
lowed by  a  dilatation  of  the  vessels,  an  increased  rapidity  of  the  circulation, 
and  an  elevation  of  temperature  in  the  anterior  and  posterior  limbs ;  gal- 
vanization of  the  peripheral  ends  of  these  nerves  causes  all  of  these  phe- 
nomena to  disappear.  Division  of  the  splanchnic  nerve  causes  a  dilatation 
of  the  blood  vessels  of  the  intestine. 

These  phenomena  of  the  sympathetic  nerve  system  are  dependent  upon 
the  presence  of  vasomotor  nerves,  which,  under  normal  circumstances,  exert 
a  tonic  influence  upon  the  blood  vessels.  These  nerves,  derived  from  the 
cerebro-spinal  system,  the  medulla- obi ongata,  leave  the  spinal  cord  by  the 
rami  communicantes,  enter  the  sympathetic  ganglia,  and  finally  terminate 
in  the  muscular  wall  of  the  blood  vessels. 

Sleep  is  a  periodical  condition  of  the  nervous  system,  in  which  there  is 
a  partial  or  complete  cessation  of  the  activities  of  the  higher  nerve  centres. 
The  cause  of  sleep  is  a  diminution  in  the  quantity  of  blood,  occasioned  by  a 
contraction  of  the  smaller  arteries  under  the  influence  of  the  vasomotor  nerves. 

During  the  waking  state  the  brain  undergoes  a  physiological  waste,  as 
a  result  of  the  exercise  of  its  functions;  after  a  certain  length  of  time  its 
activities  become  enfeebled,  and  a  period  of  repose  ensues,  during  which 
a  regeneration  of  its  substance  takes  place. 

When  the  brain  becomes  enfeebled  there  is  a  diminished  molecular 
activity  and  an  accumulation  of  waste  products ;  under  these  circumstances 
it  ceases  to  dominate  the  medulla  oblongata  and  the  spinal  cord.  These 
centres  then  act  more  vigorously,  and  diminish  the  calibre  of  the  cerebral 
blood  vessels  through  the  action  of  the  vasomoter  nerves,  producing  a  con- 
dition of  physiological  ancemia  and  sleep;  during  this  state  waste  products 
are  removed,  force  is  stored  up,  nutrition  is  restored,  and  waking  finally 
occurs. 


THE   SENSE   OF   TOUCH.  151 

THE  SENSE  OF  TOUCH. 

The  Sense  of  Touch  is  a  modification  of  general  sensibility,  and 
located  in  the  skin,  which  is  especially  adapted  for  this  purpose,  on  account 
of  the  number  of  nerves  and  papillary  elevations  it  possesses.  The  structures 
of  the  skin  and  the  modes  of  termination  of  the  sensory  nerves  have  already 
been  considered. 

The  Tactile  Sensibility  varies  in  acuteness  in  different  portions  of  the 
body ;  being  most  marked  in  those  regions  in  which  the  tactile  corpuscles 
are  most  abundant,  e,  g.,  the  palmar  surface  of  the  third  phalanges  of  the 
fingers  and  thumb. 

The  relative  sensibility  of  different  portions  of  the  body  has  been  ascer- 
tained by  means  of  a  pair  of  compasses,  the  points  of  which  are  guarded 
by  cork,  and  then  determining  how  closely  they  could  be  brought  together, 
and  yet  be  felt  at  two  distinct  points.  The  following  are  some  of  the 
measurements : — 

Point  of  tongue, ]^  of  a  line. 

Palmar  surface  of  third  phalanx, I  line. 

Red  surface  of  lips,        2  lines. 

Palmar  surface  of  metacarpus, 3 

Tip  of  the  nose, 3 

Part  of  lips  covered  by  skin, 4 

Palm  of  hand, 5 

Lower  part  of  forehead, 10 

Back  of  hand, 14 

Dorsum  of  foot, 18     " 

Middle  of  the  thigh, 30     " 

The  sense  of  touch  communicates  to  the  mind  the  idea  of  resistance  only, 
and  the  varying  degrees  of  resistance  offered  to  the  sensory  nerves  enable 
us  to  estimate,  with  the  aid  of  the  muscular  sense,  the  qualities  of  hardness 
and  softness  of  external  objects.  The  idea  of  space  or  extension  is  obtained 
when  the  sensory  surface  or  the  external  object  changes  its  place  in  regard 
to  the  other,  the  character  of  the  surface,  its  roughness  or  smoothness,  is 
estimated  by  the  impressions  made  upon  the  tactile  papillae. 

Appreciation  of  Temperature.  The  general  surface  of  the  body  is  more 
or  less  sensitive  to  differences  of  temperature,  though  this  sensation  is 
separate  from  that  of  touch ;  whether  there  are  nerves  especially  adapted 
for  the  conduction  of  this  sensation  has  not  been  fully  determined.  Under 
pathological  conditions,  however,  the  sense  of  touch  may  be  abolished,  while 
the  appreciation  of  changes  in  temperature  may  remain  normal. 


152  HUMAN    PHYSIOLOGY. 

The  cutaneous  surface  varies  in  its  sensibility  to  temperature  in  different 
parts  of  the  body,  and  depends,  to  some  extent,  upon  the  thickness  of  the 
skin,  exposure,  habit,  etc. ;  the  inner  surface  of  the  elbow  is  more  sensitive 
to  changes  in  temperature  than  the  outer  portion  of  the  arm ;  the  left  hand 
is  more  sensitive  than  the  right;  the  mucous  membrane  less  so  than  the 
skin. 

Excessive  heat  or  cold  has  the  same  effect  upon  the  sensibility  ;  the  tem- 
peratures most  readily  appreciated  are  those  between  50°  F.  and  115°  F. 

The  sensations  of  pain  and  tickling  appear  to  be  conducted  to  the  brain, 
also,  by  nerves  different  from  those  of  touch ;  in  abnormal  conditions  the 
appreciation  of  pain  may  be  entirely  lost,  while  touch  remains  unimpaired. 


THE  SENSE  OF  TASTE. 

The  Sense  of  Taste  is  localized  mainly  in  the  mucous  membrane 
covering  the  superior  surface  of  the  tongue. 

The  Tongue  is  situated  in  the  floor  of  the  mouth ;  its  base  is  directed 
backward,  and  connected  with  the  hyoid  bone,  by  numerous  muscles,  with 
the  epiglottis  and  soft  palate ;  its  apex  is  directed  forward  against  the  pos- 
terior surface  of  the  teeth. 

The  substance  of  the  tongue  is  made  up  of  intrinsic  muscular  fibres,  the 
linguales ;  it  is  attached  to  surrounding  parts,  and  its  various  movements 
performed  by  the  extrinsic  muscles,  e.  g.,  stylo-glossus,  genio-hyo-glossus, 
etc. 

The  mucous  membrane  covering  the  tongue  is  continuous  with  that  lining 
the  commencement  of  the  alimentary  canal,  and  is  furnished  with  vascular 
and  nervous  papillae. 

The  papillae  are  analogous  in  their  structure  to  those  of  the  skin,  and 
are  distributed  over  the  dorsum  of  the  tongue,  giving  it  its  characteristic 
roughness. 

There  are  three  principal  varieties : — 

1.  Tb& filiform  papilla  are  most  numerous,  and  cover  the  anterior  two- 
thirds  of  the  tongue;  they  are  conical  or  filiform  in  shape,  often  prolonged 
into  filamentous  tufts,  of  a  whitish  color,  and  covered  by  horny  epithelium. 

2.  The  fungiform  papilla  are  found  chiefly  at  the  tip  and  sides  of  the 
tongue  ;  they  are  larger  than  the  preceding,  and  may  be  recognized   by 
their  deep  red  color. 

3.  The  circumvallate  papilla  are  rounded  eminences,  from  eight  to  ten 
in  number,  situated  at  the  base  of  the  tongue,  where  they  form  a  V-shaped 


THE  SENSE  OF  TASTE.  153 

figure.  They  are  quite  large,  and  consist  of  a  central  projection  of  mucous 
membrane,  surrounded  by  a  wall,  or  circumvallation,  from  which  they 
derive  their  name. 

The  Taste  Beakers,  supposed  to  be  the  true  organs  of  taste,  are  flask- 
like  bodies,  ovoid  in  form,  about  3-^  of  an  inch  in  length,  situated  in 
the  epithelial  covering  of  the  mucous  membrane,  on  the  circumvallate 
papillce.  They  consist  of  a  number  of  fusiform,  narrow  cells,  and  curved 
so  as  to  form  the  walls  of  this  flask-like  body;  in  the  interior  are  elongated 
cells,  with  large,  clear  nuclei,  the  taste  cells. 

Nerves  of  Taste.  The  chorda  tympani  nerve,  a  branch  of  the  facial, 
after  leaving  the  cavity  of  the  tympanum,  joins  the  3d  division  of  the  5th 
nerve  between  the  two  pterygoid  muscles,  and  then  passes  forward  in  the 
lingual  branches,  to  be  distributed  to  the  mucous  membrane  of  the  anterior 
two-thirds  of  the  tongue.  Division  or  disease  of  this  nerve  is  followed  by 
a  loss  of  taste  in  the  part  to  which  it  is  distributed. 

The  glosso-pharyngeal  enters  the  tongue  at  the  posterior  border  of  the 
hyo-glossus  muscle,  and  is  distributed  to  the  mucous  membrane  of  the  base 
and  sides  of  the  tongue,  fauces,  etc. 

The  lingual  branch  of  the  trifacial  nerve  endows  the  tongue  with  gen- 
eral sensibility;  the  hypoglossal endows  it  with  motion. 

The  nerves  of  taste  in  the  superficial  layer  of  the  mucous  membrane 
form  a  fine  plexus,  from  which  branches  pass  to  the  epithelium  and  pene- 
trate it ;  others  enter  the  taste  beakers,  and  are  directly  connected  with  the 
taste  cells. 

The  seat  of  the  sense  of  taste  has  been  shown  by  experiment  to  be  the 
whole  of  the  mucous  membrane  over  the  dorsum  of  the  tongue,  soft  palate, 
fauces,  and  upper  part  of  the  pharynx. 

The  Sense  of  Taste  enables  us  to  distinguish  the  savor  of  substances 
introduced  into  the  mouth,  which  is  different  from  tactile  sensibility.  The 
sapid  quality  of  substances  appreciated  by  the  tongue  are  designated  as 
bitter,  sweet,  alkaline,  sour,  salt,  etc. 

The  Essential  Conditions  for  the  production  of  the  impressions  of 
taste  are  (i)  a  state  of  solubility  of  the  food  ;  (2)  a  free  secretion  of  the 
saliva,  and  (3)  active  movements  on  the  part  of  the  tongue,  exciting  pres- 
sure against  the  roof  of  the  mouth,  gums,  etc.,  thus  aiding  the  solution  of 
various  articles  and  their  osmosis  into  the  lingual  papillae.  Sapid  substances, 
when  in  a  state  of  solution,  pass  into  the  interior  of  the  taste  beakers,  and 
come  into  contact,  through  the  medium  of  the  taste  cells,  with  the  terminal 
filaments  of  the  gustatory  nerves. 
K 


154  HUMAN   PHYSIOLOGY. 

THE  SENSE  OF  SMELL. 

The  Sense  of  Smell  is  located  in  the  mucous  membrane  lining  the 
upper  part  of  the  nasal  cavity,  in  which  the  olfactory  nerves  are  distributed. 

The  Nasal  Fossae  are  two  cavities,  irregular  in  shape,  separated  by 
the  vomer,  the  perpendicular  plate  of  the  ethmoid  bone,  and  the  triangular 
cartilage.  They  open  anteriorly  and  posteriorly  by  the  anterior  and  pos- 
terior nares,  the  latter  communicating  with  the  pharynx.  They  are  lined 
by  mucous  membrane,  of  which  the  only  portion  capable  of  receiving 
odorous  impressions  is  the  part  lining  the  upper  one-third  of  the  fossse. 

The  Olfactory  Nerves,  arising  by  three  roots  from  the  posterior  and 
inferior  surface  of  the  anterior  lobes,  pass  forward  to  the  cribriform  plate 
of  the  ethmoid  bone,  where  they  each  expand  into  an  oblong  body,  the 
olfactory  bulb.  From  its  under  surface  from  fifteen  to  twenty  filaments  pass 
downward  through  the  foramina,  to  be  distributed  to  the  olfactory  mucous 
membrane,  where  they  terminate  in  long,  delicate,  spindle-shaped  cells, 
the  olfactory  cells,  situated  between  the  ordinary  epithelial  cells. 

The  olfactory  bulbs  are  the  centres  in  which  odorous  impressions  are 
perceived  as  sensations ;  destruction  of  these  bulbs  being  attended  by  an 
abolition  of  the  sense  of  smell. 

In  animals  which  possess  an  acute  sense  of  smell,  there  is  a  correspond- 
ing increase  in  the  development  of  the  olfactory  bulbs. 

The  Essential  Conditions  for  the  sense  of  smell  are,  (i)  a  special 
nerve  centre  capable  of  receiving  impressions  and  transforming  them  into 
odorous  sensations.  (2)  Emanations  from  bodies  which  are  in  a  gaseous 
or  vaporous  condition.  (3)  The  odorous  emanations  must  be  drawn  freely 
through  the  nasal  fossae ;  if  the  odor  be  very  faint,  a  peculiar  inspiratory 
movement  is  made,  by  which  the  air  is  forcibly  brought  into  contact  with 
the  olfactory  filaments.  The  secretions  of  the  nasal  fossae  probably  dissolve 
the  odorous  particles. 

Various  substances,  as  ammonia,  horseradish,  etc.,  excite  the  sensibility 
of  the  mucous  membrane,  which  must  be  distinguished  from  the  perception 
of  true  odors. 

THE  SENSE  OF  SIGHT. 

The  Eyeball.  The  eyeball  or  organ  of  vision  is  situated  at  the  fore 
part  of  the  orbital  cavity  and  supported  by  a  cushion  of  fat;  it  is  protected 
from  injury  by  the  bony  walls  of  the  cavity,  the  lids  and  lashes,  and  is  so 


THE   SENSE   OF   SIGHT.  155 

situated  as  to  permit  of  an  extensive  range  of  vision.  The  eyeball  is  loosely 
held  in  position  by  a  fibrous  membrane,  the  capsule  of  Tenon,  which  is 
attached  on  the  one  hand  to  the  eyeball  itself  and  on  the  other  to  the  walls 
of  the  cavity.  Thus  suspended,  the  eyeball  is  capable  of  being  moved  in 
any  direction  by  the  contraction  of  the  muscles  attached  to  it. 

Structure.  The  eyeball  is  spheroidal  in  shape  and  measures  about  nine- 
tenths  of  an  inch  in  its  antero-posterior  diameter,  and  a  little  less  in  its 
transverse  diameter.  When  viewed  in  profile  it  is  seen  to  consist  of  the 
segments  of  two  spheres,  of  which  the  posterior  is  the  larger,  occupying 
five-sixths,  and  the  anterior  the  smaller,  occupying  one-sixth  of  the  ball. 

The  eye  is  made  up  of  several  membranes  concentrically  arranged,  within 
which  are  enclosed  the  refracting  media  essential  to  vision.  These  mem- 
branes enumerated  from  without  inwards,  are  :  1st,  the  sclerotic  and  cornea ; 
2d,  the  choroid  and  iris;  3d,  the  retina;  the  refracting  media  are  the 
aqueous  humor,  the  crystalline  lens  and  vitreous  humor. 

The  Sclerotic  and  Cornea.  The  sclerotic  is  the  opaque  fibrous  mem- 
brane covering  the  posterior  five-sixths  of  the  ball.  It  is  composed  of  con- 
nective tissue  arranged  in  layers  which  run  both  transversely  and  longitudi- 
nally; it  is  pierced  posteriorly  by  the  optic  nerve  about  one-tenth  of  an 
inch  internal  to  the  optic  axis.  The  sclerotic  by  its  density  gives  form  to 
the  eye  and  protects  the  delicate  structures  within  it,  and  serves  for  the 
attachment  of  the  muscles  by  which  the  ball  is  moved. 

The  cornea  is  a  transparent  non-vascular  membrane  covering  the  anterior 
one-sixth  of  the  eyeball.  It  is  nearly  circular  in  shape  and  is  continuous  at 
the  circumference  with  the  sclerotic,  from  which  it  cannot  be  separated. 
The  substance  of  the  cornea  is  made  up  of  thin  layers  of  delicate  trans- 
parent fibrils  of  connective  tissue  more  or  less  united  together;  between 
these  layers  are  found  a  number  of  inter-communicating  lymph  spaces  lined 
by  endothelium,  which  are  in  connection  with  lymphatics.  Leucocytes  or 
lymph  corpuscles  are  often  found  in  these  spaces.  The  anterior  surface  of 
the  cornea  is  covered  by  several  layers  of  nucleated  epithelium  which  rest 
upon  a  structureless  membrane  known  as  the  anterior  elastic  lamina.  The 
posterior  surface  is  covered  by  a  similar  membrane,  the  membrane  of 
Decemet,  which  becomes  continuous  at  its  periphery  with  the  iris;  it  is  also 
covered  by  a  layer  of  epithelial  cells.  At  the  junction  of  the  cornea  and 
sclerotic  is  found  a  circular  groove,  the  canal  of  Schlemm. 

The  Choroid,  the  Iris,  the  Ciliary  Muscle  and  Ciliary  processes, 
together  constitute  the  second  or  middle  coat  of  the  eyeball. 

The  choroid  is  a  dark  brown  membrane  which  extends  forward  nearly 


156  HUMAN   PHYSIOLOGY. 

to  the  cornea,  where  it  terminates  in  a  series  of  folds,  the  ciliary  processes. 
In  its  structure  the  choroid  is  highly  vascular,  consisting.of  both  arteries  and 
veins.  Externally  it  is  connected  with  the  sclerotic  by  connective  tissue ; 
internally  it  is  lined  by  a  layer  of  hexagonal  pigment  cells  which,  though 
usually  classed  as  belonging  to  the  choroid,  is  now  known  to  belong  embryo- 
logically  and  physiologically  to  the  retina.  From  without  inward  may  be 
distinguished  the  following  layers  : — 

1.  The  lamina  supra-choroidea. 

2.  The  elastic  layer  of  Sattler,  consisting  of  two  endothelial  layers. 

3.  The    chorio-capilfaris,  choroid    proper,  or  membrane  of  Ruysch,  a 

thick  elastic  network  of  arterioles  and  capillaries  lying  within  the 
,  outer  layer  of  veins  and  arteries  called  the  vena  vorticosse. 

4.  The  lamina  vitrea  or  internal  limiting  membrane. 

The  choroid  with  its  contained  blood  vessels  bears  an  important  relation  to 
the  nutrition  of  the  eye ;  it  provides  for  the  blood  supply,  for  drainage  from 
the  body  of  the  eye,  and  presents  an  uniform  and  high  temperature  to  the 
retina. 

The  Iris  is  the  circular  variously-colored  membrane  placed  in  the  an- 
terior portion  of  the  eye  just  behind  the  cornea.  It  is  perforated  a  little  to 
the  nasal  side  of  the  centre  by  a  circular  opening,  the  pupil.  The  outer 
or  circumferential  border  is  connected  with  the  cornea,  ciliary  muscle  and 
ciliary  processes ;  the  free  inner  edge  forms  the  boundary  of  the  pupil,  the 
size  of  which  is  constantly  changing.  The  framework  of  the  iris  is  com- 
posed of  connective  tissue,  blood  vessels,  muscular  fibres  and  pigmented 
connective-tissue  corpuscles.  The  anterior  surface  is  covered  with  a  layer 
of  epithelial  cells  continuous  with  those  covering  the  posterior  surface  of 
the  cornea;  the  posterior  surface  is  lined  by  a  limiting  membrane  bearing 
pigment  epithelial  cells  continuous  with  those  of  the  choroid.  The  various 
colors  which  the  iris  assumes  in  different  individuals  depend  upon  the 
quantity  and  disposition  of  the  pigmentary  granules. 

The  muscular  fibres  of  the  iris,  which  are  of  the  non-striated  variety,  are 
arranged  in  two  sets, — the  sphincter  and  dilator. 

The  sphincter  pupillce  is  a  circular  flat  band  of  muscular  fibres  surround- 
ing the  pupil  close  to  its  posterior  surface ;  by  its  contraction  and  relaxa- 
tion, the  pupil  is  diminished  or  increased  in  size.  The  dilator  pupilla 
consists  of  a  thin  layer  of  fibres  arranged  in  a  radiate  manner ;  at  the  mar- 
gin of  the  pupil  they  blend  with  those  of  the  sphincter  muscle,  while  at  the 
outer  border  they  arch  to  form  a  circular  muscular  layer. 

T\\z  ciliary  muscle  is  a  gray  circular  band  consisting  of  unstriped  muscu- 
lar fibres  about  one-tenth  of  an  inch  long  running  from  before  backward. 


THE   SENSE   OF   SIGHT. 


157 


It  is  attached  anteriorly  to  the  inner  surface  of  the  sclerotic  and  cornea, 
and  posteriorly  to  the  choroid  coat  opposite  the  ciliary  processes.  At  the 
anterior  border  of  the  radiating  fibres  and  internally  are  found  bundles  of 
circular  muscular  fibres,  constituting  the  annular  muscle  of  Miiller.  The 
ciliary  muscle  thus  consists  of  two  sets  of  fibres,  a  radiating  and  circular, 
both  of  which  are  concerned  in  effecting  a  change  in  the  convexity  of  the 
lens  in  the  accommodation  of  the  eye  to  near  vision. 

The  Retina  forms  the  internal  coat  of  the  eye.     In  the  fresh  state  it  is  a 
delicate  transparent  membrane  of  a  pink  color,  but  after  death  soon  becomes 


FIG.  20. 


d  - 


SCLEROTIC    COAT    REMOVED    TO    SHOW    THE    CHOROID,    CILIARY    MUSCLE    AND    NERVES. 

a.  Sclerotic  coat.     b.  Veins  of  the  choroid.     c.  Ciliary  nerves,    d.  Veins  of  the  choroid. 
e.  Ciliary  muscle,   f.  Iris. — From  Holden's  Anatomy. 

opaque;  it  extends  forward  almost  to  the  ciliary  processes,  where  it  termi- 
nates in  an  indented  border,  the  ora  serrata.  In  the  posterior  part  of  the 
retina  at  a  point  corresponding  to  the  axis  of  vision  is  a  yellow  spot,  the 
macula  lutea,  which  is  somewhat  oval  in  shape  and  tinged  with  yellow 
pigment.  It  presents  in  its  centre  a  depression,  the  fovea  centralis,  corres- 
ponding to  a  decrease  in  thickness  of  the  retina ;  about  one-tenth  of  an 
inch  to  the  inner  side  of  the  macula  is  the  point  of  entrance  of  the  optic 
nerve.  The  arleria  centralis  retince  pierces  the  optic  nerve  near  the 
sclerotic,  runs  forward  in  its  substance  and  is  distributed  in  the  retina  as  far 
forward  as  the  ciliary  processes. 


158  HUMAN    PHYSIOLOGY. 

The  retina  is  remarkably  complex,  consisting  of  ten  distinct  layers,  from 
within  outward,  supported  by  connective  tissue.  These  are  as  follows, 
viz.:  i.  Membrana  limitans  interna.  2.  Fibres  of  optic  nerve.  3. 
Layers  of  ganglionic  corpuscles,  4.  Molecular  layer.  5.  Internal  granu- 
lar layer.  6.  Molecular  layer.  7.  External  granular  layer.  8.  Mem- 
brana limitans  externa.  9.  Jacobson's  membrane  or  layer  of  rods  and  cones. 
10.  The  layer  of  pigment  cells. 

The  most  important  of  these,  however,  is  the  layer  of  rods  and  cones  in 
the  external  portion  of  the  retina.  The  rods  are  straight  elongated  cylinders 
extending  through  the  entire  thickness  of  Jacobson's  membrane.  They 
consist  of  an  external  portion  which  is  clear,  homogeneous  and  highly  re- 
fracting, and  of  an  internal  portion  which  is  slightly  granular  and  less 
refractive;  the  outer  end  of  each  rod  is  in  direct  contact  with  the  pig- 
mentary epithelium  lining  the  choroid,  while  the  inner  end  tapering  to  a  fine 
thread,  pierces  the  external  limiting  membrane  and  passes  into  the  external 
granular  layer.  The  cones  consist  also  of  two  portions,  the  inner  of  which 
is  somewhat  thicker  than  the  rod  and  rests  upon  the  limiting  membrane ; 
the  outer  portion  tapers  to  a  fine  point  which  is  known  as  the  cone-style. 
The  cones,  as  a  rule,  are  somewhat  shorter  than  the  rods.  The  propor- 
tion of  rods  to  cones  varies  in  different  parts  of  the  retina,  though  there  are 
on  the  average  about  fourteen  rods  to  one  cone.  In  the  macula  lutea,  where 
vision  is  most  acute,  the  rods  are  almost  entirely  absent,  cones  alone  being 
present.  All  the  retinal  elements  at  this  point  are  changed.  The  nerve 
fibre  layer  is  absent,  the  axis  cylinders  radiating  in  such  a  manner  as  to 
leave  the  spot  free  from  their  covering.  The  remaining  layers  are  all 
thinned  and  the  stroma  reduced  to  a  minimum.  The  optic  nerve  after 
passing  forward  from  the  brain  penetrates  in  succession  the  sclerotic, 
choroid,  and  retina  ;  the  nerve  fibres  then  spread  out  over  the  anterior 
surface  of  the  retina  and  become  connected  with  the  large  ganglionic  cells, 
the  third  layer  of  the  retina. 

The  number  of  optic  nerve  fibres  in  the  retina  is  estimated  to  be  about 
800,000,  and  for  each  fibre  there  are  about  seven  cones,  one  hundred  rods, 
and  seven  pigment  cells.  The  points  of  the  rods  and  cones  are  directed 
toward  the  choroid,  or  away  from  the  entering  light,  and  dip  into  the  pig- 
mentary layer.  They,  with  the  pigment  layer,  are  the  elements  interme- 
diating the  change  of  the  ethereal  vibrations  into  nerve  force;  out  of  these 
nerve  vibrations  the  brain  fashions  the  sensations  of  light,  form  and  color. 

The  vitreous  humor,  which  supports  the  retina,  is  the  largest  of  the  re- 
fracting media;  it  is  globular  in  form  and  constitutes  about  four-fifths  of  the 
ball ;  it  is  hollowed  out  anteriorly  for  the  reception  of  the  crystalline  lens. 


THE   SENSE   OF   SIGHT.  159 

The  outer  surface  of  the  vitreous  is  covered  by  a  delicate  transparent  mem- 
brane, termed  the  hyaloid  membrane,  which  serves  to  maintain  its  globular 
form. 

The  aqueous  humor  found  in  the  anterior  chamber  of  the  eye  is  a  clear 
alkaline  fluid,  having  a  specific  gravity  of  1.003-1.009.  It  is  secreted  most 
probably  by  the  blood  vessels  of  the  iris  and  ciliary  processes.  It  passes 
from  the  interior  of  the  eye,  through  the  canal  of  Schlemm  and  the  meshes 
at  the  base  of  the  iris,  into  the  anterior  circular  vein. 

The  crystalline  lens  enclosed  within  its  capsule,  is  a  transparent  bi-con- 
vex  body,  situated  just  behind  the  iris  and  resting  in  the  depression  in  the 
anterior  part  of  the  vitreous.  The  two  convexities  are  not  quite  alike,  the 
curvature  of  the  posterior  surface  being  slightly  greater  than  that  of  the  an- 
terior. The  lens  measures  about  one-third  of  an  inch  in  the  transverse 
diameter  and  one-fifth  of  an  inch  in  the  antero-posterior  diameter. 

The  suspensory  ligament,  by  which  the  lens  is  held  in  position,  is  a  firm 
transparent  membrane,  united  to  the  ciliary  processes.  A  short  distance 
beyond  its  origin,  it  splits  into  two  layers,  the  anterior  of  which  is  inserted 
into  the  capsule  of  the  lens  and  blends  with  it ;  the  posterior  passing  inward 
behind  the  lens,  becomes  united  to  its  capsule.  The  anterior  layer  pre- 
sents a  series  of  foldings,  Zone  of  Zinn,  which  are  inserted  into  the  intervals 
of  the  folds  of  the  ciliary  processes.  The  triangular  space  between  the  two 
layers  is  the  canal  of  Petit. 

Blood  vessels  and  Nerves.  The  structures  composing  the  eyeball  are 
supplied  with  blood  by  the  long  and  short  ciliary  arteries,  branches  of  the 
ophthalmic ;  they  pierce  the  sclerotic  at  various  points  and  are  ultimately 
distributed  to  all  tissues  within  the  ball. 

The  nerve  supply  comes  largely  from  the  ophthalmic  or  ciliary  ganglion. 
This  is  a  small  body,  situated  in  the  posterior  part  of  the  orbit;  it  receives 
motor  fibres  from  a  branch  of  the  motor- oculi,  or  third  nerve;  a  sensory 
branch  from  the  ophthalmic  division  of  the  fifth  nerve  and  fibres  from  the 
cavernous  plexus  of  the  sympathetic.  From  the  anterior  border  of  the 
ganglion  proceed  the  ciliary  nerves  which,  entering  the  eyeball,  endow  its 
structures  with  motion  and  sensation. 

The  Eyeball  a  Living  Camera  Obscura.  The  eyeball  may  be  com- 
pared in  a  general  way  to  a  camera  obscura.  The  anatomical  arrangement 
of  its  structures  reveal  many  points  of  similarity.  The  sclerotic  and  choroid 
may  be  compared  with  the  walls  of  the  chamber;  the  combined  refractive 
media,  cornea,  aqueous  humor,  lens,  and  vitreous  humor,  to  the  lens  for 
focusing  the  rays  of  light ;  the  retina  to  the  sensitive  plate  receiving  the 


160 


HUMAN    PHYSIOLOGY. 


image  formed  at  the  focal  point ;  the  iris  to  the  diaphragm,  which  by  cutting 
off  the  marginal  rays  prevents  spherical  aberration  and  at  the  same  time 
regulates  the  amount  of  light  entering  the  eye;  the  ciliary  muscle  to  the 
adjusting  screw  by  which  distinct  images  are  thrown  upon  the  retina  in  spite 
of  varying  distances  of  the  object  from  which  the  light  rays  emanate.  The 
structures  just  enumerated  are  those  essential  for  normal  vision. 

The  relationship  of  the  various  structures  composing  the  eyeball  is  shown 
by  the  following  figure  : — 


DIAGRAM    OF    A   VERTICAL   SECTION    OF   THE    EYE. 

i.  Anterior  chamber  filled  with  aqueous   humor.     2.  Posterior  Chamber.     3.  Canal  o* 

Petit. 
a.     Hyaloid    membrane,     b.     Retina    (dotted    line),     c.     Choroid    coat    (black   line). 

d.  Sclerotic  coat.     e.  Cornea,   f.  Iris.    g.  Ciliary  processes,     h.  Canal  of  Schlemm 

or  Fontana.     /.  Ciliary  muscle. — From  Holden'  s  Anatomy. 

The  Dioptric  or  Refracting  apparatus  by  which  the  rays  of  light  enter- 
ing the  eye  are  so  manipulated  as  to  produce  an  image  on  the  retina, 
consists  of  the  cornea,  aqueous  humor,  crystalline  lens  and  vitreous  humor. 
A  ray  of  light  in  passing  through  each  of  these  media  will  undergo  refrac- 
tion at  their  surfaces  and  ultimately  be  brought  to  a  focus  at  the  retina. 
Inasmuch  as  the  two  surfaces  of  the  cornea  are  parallel  and  its  refractive 
power  practically  the  same  as  the  aqueous  humor,  the  media  may  be  re- 
duced to  three,  viz :  I.  Cornea  and  aqueous  humor.  2.  The  lens.  3. 
The  vitreous  humor.  The  refracting  surfaces  may  also  be  reduced  to  three, 


THE   SENSE   OF   SIGHT. 


161 


viz  :   i.  Anterior  surface  of  the  cornea.     2.  Anterior  surface  of  lens.     3. 
Posterior  surface  of  lens. 

The  refraction  effected  by  the  cornea  is  very  great,  owing  to  the  passage 
of  the  light  from  the  air  into  a  comparatively  dense  medium,  and  is  sufficient 
of  itself  to  bring  parallel  rays  of  light  to  a  focus  about  10  millimetres  behind 
the  retina.  This  would  be  the  condition  in  an  eye  in  which  the  lens  was 
congenitally  absent.  Perfect  vision  requires,  however,  that  the  convergence 
of  the  light  shall  be  great  enough  that  the  image  may  fall  upon  the  retina. 
This  is  accomplished  by  the  crystalline  lens,  a  body  denser  than  the  cornea 
and  possessing  a  higher  refractive  power.  The  manner  in  which  a  biconvex 
lens  focuses  both  parallel  and  divergent  rays  is  shown  in  the  following 
figures : — 

FIG.  22. 


DIAGRAM  SHOWING  THE  COURSE  OF  PARALLEL  RAYS  OF  LIGHT  FROM  A  IN  THEIR  PASSAGE 
THROUGH    A    BICONVEX    LENS     L,     IN    WHICH    THEY    ARE    SO    REFRACTED    AS    TO    BEND 

TOWARD  AND  COME  TO  A  FOCUS  AT  A  POINT  F '.—From  Yeo' s  Text-Book  of  Physiology. 
FIG.  23. 


DIAGRAM   SHOWING    THE   COURSE   OF     DIVERGING    RAYS    WHICH    ARE   BENT   TO    A   POINT 
FURTHER    FROM  THE  LENS  THAN  THE    PARALLEL  RAYS   IN  PRECEDING  FIGURE. — From 

Yea's  Text-Book  of  Physiology. 


The  function  of  the  crystalline  lens,  therefore,  is  to  focus  the  rays  of  light 
with  the  formation  of  an  image  on  the  retina. 

The  Retinal  Image  corresponds  in  all  respects  to  the  object  from  which 
the  light  proceeds.  The  existence  of  this  image  can  be  demonstrated  by 
removing  from  the  eye  of  a  recently  killed  animal  a  circular  portion  of  the 
sclerotic  and  choroid  posteriorly  and  then  placing  at  the  proper  distance  in 
front  of  the  cornea  a  lighted  candle  ;  an  inverted  image  of  the  candle  will  be 


162  HUMAN    PHYSIOLOGY. 

seen  upon  the  retina.  The  size  of  the  retinal  image  depends  upon  the 
visual  angle,  which  in  turn  depends  upon  the  size  of  the  object  and  its 
distance  from  the  eye.  At  a  distance  of  15.2596  metres  the  image  of  an 
object  I  metre  high  would  be  I  millimetre,  or  a  thousand  times  smaller  than 
the  object. 

Accommodation.  By  accommodation  is  understood  the  power  which 
the  eye  possesses  of  adjusting  itself  to  vision  at  different  distances.  In  a 
normal  or  emmetropic  eye  parallel  rays  of  light  are  brought  to  a  focus  on 
the  retina ;  but  divergent  rays,  that  is  rays  coming  from  a  near  luminous 
point,  will  be  brought  to  a  focus  behind  the  retina,  provided  the  refractive 
media  remain  the  same ;  as  a  result  vision  would  be  indistinct,  from  the 
formation  of  diffusion  circles.  It  is  impossible  to  see  distinctly,  therefore, 
a  near  and  distant  object  at  the  same  time.  We  must  alternately  direct 
the  vision  from  one  to  the  other.  A  normal  eye  does  not  require  adjust- 
ing for  parallel  rays ;  but  for  divergent  rays  a  change  in  the  eye  is  necessi- 
tated ;  this  is  termed  accommodation.  In  the  accommodation  for  near 
vision  the  lens  becomes  more  convex,  particularly  on  its  anterior  surface ; 
the  increase  in  convexity  increases  its  refractive  power ;  the  greater  the 
degree  of  divergence  of  the  rays  previous  to  entering  the  eye,  the  greater 
the  increase  of  convexity  of  the  lens  and  convergence  of  the  rays  after 
passing  through  it.  By  this  alteration  in  the  shape  of  the  lens  we  are 
enable  to  focus  light  rays  coming  from,  and  to  see  distinctly,  near  as  well 
as  distant  objects. 

Function  of  the  Ciliary  Muscle.  Though  it  is  admitted  that  the 
change  in  the  convexity  of  the  lens  is  caused  by  the  contraction  of  the 
ciliary  muscle  and  the  relaxation  of  the  suspensory  ligament,  the  exact  manner 
in  which  it  does  so  is  not  understood.  When  the  eye  is  in  repose  as  in 
distant  vision,  the  suspensory  ligament  is  tense  and  the  lens  possesses  that 
degree  of  curvature  necessary  for  focusing  parallel  rays.  In  the  voluntary 
efforts  to  accommodate  the  eye  for  near  vision,  the  ciliary  muscle  contracts, 
the  suspensory  ligament  relaxes  and  the  lens,  inherently  elastic,  bulges  for- 
ward and  once  again  focuses  the  rays  upon  the  retina.  It  is,  therefore, 
termed  the  muscle  of  accommodation,  and  by  its  alternate  contraction  and 
relaxation  the  lens  is  rendered  more  or  less  convex,  according  to  the 
requirements  for  near  and  distant  vision. 

Range  of  accommodation.  Parallel  rays  coming  from  a  luminous 
point,  distant  not  less  than  200  feet,  do  not  require  adjustment :  from  this 
point  up  to  infinity  no  accommodation  is  required  for  perfect  vision.  This 
is  termed  \\iepunctum  remotum,  and  indicates  the  distance  to  which  an  object 


THE   SENSE   OF   SIGHT.  163 

may  be  removed  and  yet  distinctly  seen.  If  the  object  be  brought  nearer 
to  the  eye  than  200  feet  the  accommodative  power  must  come  into  play : 
the  nearer  the  object  the  more  energetic  must  be  the  contraction  of  the 
ciliary  muscle  and  the  consequent  increase  in  the  convexity  of  the  lens.  At 
a  distance  of  five  inches,  however,  the  power  of  accommodation  reaches  its 
maximum  :  this  is  termed  the  punctum  proximum,  and  indicates  the  nearest 
point  at  which  an  object  may  be  seen  distinctly.  The  distance  between 
these  two  points  is  the  range  of  accommodation. 

Optical  Defects.  Astigmatism  is  a  condition  of  the  eye  which 
prevents  vertical  and  horizontal  lines  from  being  focused  at  the  same 
time,  and  is  due  to  a  greater  curvature  of  the  cornea  in  one  meridian 
than  another. 

Spherical  aberration  is  a  condition  in  which  there  is  an  indistinctness  of 
an  image  from  the  unequal  refraction  of  the  rays  of  light  passing  through 
the  circumference  and  the  centre  of  the  lens;  it  is  corrected  mainly  by  the 
iris,  which  cuts  off  the  marginal  rays,  and  only  transmits  those  passing 
through  the  centre. 

Chromatic  aberration  is  a  condition  in  which  the  image  is  surrounded  by 
a  colored  margin,  from  the  decomposition  of  the  rays  of  light  into  their 
elementary  parts. 

Myopia,  or  short-sightedness,  is  caused  by  an  abnormal  increase  in  the 
antero-posterior  diameter  of  the  eyeball,  or  by  a  subnormal  refracting  power 
of  the  lens;  it  is  generally  due  to  the  first  cause;  the  lens  being  too  far 
removed  from  the  retina,  forms  the  image  in  front  of  it,  and  the  perception 
becomes  dim  and  blurred.  Concave  glasses  correct  this  defect,  by  prevent- 
ing the  rays  from  converging  too  soon. 

Hyper  met  ropia,  or  long-sightedness,  is  caused  by  a  shortening  of  the 
antero-posterior  diameter,  or  by  an  excessive  refractive  power  of  the  lens ; 
the  focus  of  the  rays  of  light  would,  therefore,  be  behind  the  retina.  Con- 
vex glasses  correct  this  defect,  by  converging  the  rays  of  light  more  anteri- 
orly. 

Presbyopia  is  a  loss  of  the  power  of  accommodation  of  the  eye  to  near 
objects,  and  usually  occurs  between  the  ages  of  40  and  60 ;  it  is  remedied  by 
the  use  of  convex  glasses. 

The  Iris.  The  iris  plays  the  part  of  a  diaphragm,  and  by  means  of  its 
central  aperture  the  pupil  regulates  the  quantity  of  light  entering  the 
interior  of  the  eye  ;  by  preventing  rays  from  passing  through  the  margin  of 
the  lens  it  diminishes  spherical  aberration.  The  size  of  the  pupil  depends 
upon  the  relative  degree  of  contraction  of  the  circular  and  radiating  fibres ; 


164  HUMAN   PHYSIOLOGY. 

the  variations  in  size  of  the  pupil  from  variations  in  the  degree  of  contrac- 
tion depend  upon  different  intensities  of  light.  If  the  light  be  intense  the 
circular  fibres  contract  and  diminish  the  size  of  the  pupil;  if  the  light 
diminishes  in  intensity  the  circular  fibres  relax  and  the  pupil  enlarges. 

Point  of  most  distinct  Vision.  While  all  portions  of  the  retina  are 
sensitive  to  light,  their  sensibility  varies  within  wide  limits.  At  the  macula 
lutea  and  more  especially  in  its  most  central  depression,  the  fovea,  where 
the  retinal  elements  are  reduced  practically  to  the  layer  of  rods  and  cones, 
the  sensibility  reaches  its  maximum.  It  is  at  this  point  that  the  image  is 
found  when  vision  is  most  distinct.  The  macula  and  fovea  are  always  in 
the  line  of  direct  vision.  From  the  macula  towards  the  periphery  of  the 
retina  there  is  a  gradual  diminution  in  sensibility  and  a  corresponding  decline 
in  the  distinctness  of  vision.  In  those  portions  of  the  retina  lying  outside 
the  macula,  the  indistinctness  of  vision  depends  not  only  on  diminished 
sensibility,  but  also  upon  inaccurate  focusing  of  the  rays. 

Blind  Spot.  Although  the  optic  nerve  transmits  the  impulses  excited 
in  the  retina  by  the  ethereal  vibration,  the  nerve  fibres  themselves  are  insen- 
sitive to  light.  At  the  point  of  entrance  of  the  optic  nerve,  owing  to  the 
absence  of  the  rods  and  cones,  the  rays  of  light  make  no  impression.  This 
is  the  blind  spot.  As  this  spot  is  not  in  the  line  of  vision,  no  dark  point  is 
ordinarily  observed  in  the  field  of  vision,  that  circular  space  before  a  fixed 
eye  within  which  objects  are  perceptible. 

The  rods  and  cones  are  the  most  sensitive  portions  of  the  retina.  A  ray 
of  light  entering  the  eye  passes  entirely  through  the  various  layers  of  the 
retina  and  is  arrested  only  upon  reaching  the  pigmentary  epithelium  in 
which  the  rods  and  cones  are  imbedded.  As  to  the  manner  in  which  the 
objective  stimuli,  light  and  color  so-called,  are  transformed  into  nerve  im- 
pulses, but  little  is  known.  It  is  probable  that  the  ethereal  vibrations  are 
transformed  into  heat,  which  excites  the  rods  and  cones.  These  acting  as 
highly  specialized  end  organs  of  the  optic  nerve,  start  the  impulses  on  their 
way  to  the  brain  where  the  seeing  process  takes  place.  As  to  the  relative 
function  of  the  rods  and  cones,  it  has  been  suggested,  from  the  study 
of  the  facts  of  comparative  anatomy,  that  the  rods  are  impressed  only  by 
differences  in  the  intensity  of  light,  while  the  cones  in  addition  are  im- 
pressed by  qualitative  differences  or  color. 

Accessory  Structures.  The  muscles  which  move  the  eyeball  are  six 
in  number;  the  superior  and  inferior  recti,  the  external  and  internal  recti, 
the  superior  and  inferior  oblique  muscles.  The  four  recti  muscles,  arising 
from  the  apex  of  the  orbit,  pass  forward  and  are  inserted  into  the  sides  of 


THE  SENSE  OF   HEARING.  165 

the  sclerotic  coat ;  the  superior  and  inferior  muscles  rotate  the  eye  around 
a  horizontal  axis ;  the  external  and  internal  rotate  it  around  a  vertical 
axis. 

The  Superior  oblique  muscle,  having  the  same  origin,  passes  forward  to 
the  inner  and  upper  angle  of  the  orbital  cavity,  where  its  tendon  passes 
through  a  cartilaginous  pulley;  it  is  then  reflected  backward  and  inserted 
into  the  sclerotic  just  behind  the  transverse  diameter.  Its  function  is  to 
rotate  the  eyeball  in  such  a  manner  as  to  direct  the  pupil  downward  and 
outward. 

The  Inferior  oblique  muscle  arises  at  the  inner  angle  of  the  orbit  and 
then  passes  outward  and  backward,  to  be  inserted  into  the  sclerotic.  Its 
function  is  to  rotate  the  eyeball  and  direct  the  pupil  upward  and  outward. 

By  the  associated  action  of  all  these  muscles,  the  eyeball  is  capable  of 
performing  all  the  varied  and  complex  movements  necessary  for  distinct 
vision. 

The  Eyelids,  bordered  with  short,  stiff  hairs,  shade  the  eye  and  protect 
it  from  injury.  On  the  posterior  surface,  just  beneath  the  conjunctiva,  are 
the  Meibomian  glands,  which  secrete  an  oily  fluid ;  it  covers  the  edge  of 
the  lids,  and  prevents  the  tears  from  flowing  over  the  cheek. 

The  Lachrymal  Glands  are  ovoid  in  shape,  and  situated  at  the  upper 
and  outer  part  of  the  orbital  cavity ;  they  open  by  from  six  to  eight  ducts 
at  the  outer  portion  of  the  upper  lids. 

The  Tears,  secreted  by  the  lachrymal  glands,  are  distributed  over  the 
cornea  by  the  lids  during  the  act  of  winking,  and  keep  it  moist  and  free 
from  dust.  The  excess  of  tears  passes  into  the  lachrymal  ducts,  which 
begin  by  two  minute  orifices,  one  on  each  lid,  at  the  inner  canthus.  They 
conduct  the  tears  into  the  nasal  duct,  and  so  into  the  nose. 


THE  SENSE  OF  HEARING. 

The  Ear  or  Organ  of  Hearing  is  lodged  within  the  petrous  portion 
of  the  temporal  bone.  It  may  be,  for  convenience  of  description,  divided 
into  three  portions,  viz :  I.  The  external  ear.  2.  The  middle  ear.  3. 
The  internal  ear  or  labyrinth. 

The  External  Ear  consists  of  the  pinna  or  auricle  and  the  external  au- 
ditory canal.  The  pinna  consists  of  a  thin  layer  of  cartilage,  presenting  a 
series  of  elevations  and  depressions ;  it  is  attached  by  fibrous  tissue  to  the 
outer  bony  edge  of  the  auditory  canal ;  it  is  covered  by  a  layer  of  integu- 
ment continuous  with  that  covering  the  side  of  the  head.  The  general 


166  HUMAN    PHYSIOLOGY. 

shape  of  the  pinna  is  concave  and  presents  a  little  below  the  centre  a  deep 
depression,  the  concha.  The  external  auditory  canal  extends  from  the 
concha  inward  for  a  distance  of  about  one  and  a  quarter  inches.  It  is 
directed  somewhat  forward  and  upward,  passing  over  a  convexity  of  bone, 
and  then  dips  downward  to  its  termination ;  it  is  composed  of  both  bone 
and  cartilage  and  lined  by  a  reflection  of  the  skin  covering  the  pinna.  At 
the  external  portion  of  the  canal  the  skin  contains  a  number  of  tubular 
glands,  the  ceruminous  glands,  which  in  their  conformation  resemble  the 
perspiratory  glands.  They  secrete  the  cerumen  or  ear  wax. 

The  Middle  Ear  or  Tympanum  is  an  irregularly  shaped  cavity  hollowed 
out  of  the  temporal  bone  and  situated  between  the  external  ear  and  the 
labyrinth.  It  is  narrow  from  side  to  side  but  relatively  long  in  its  vertical 
and  antero- posterior  diameters;  it  is  separated  from  the  external  auditory 
canal  by  a  membrane,  the  membrana  tympani  ;  from  the  internal  ear  it  is 
separated  by  an  osseo-membranous  partition  which  forms  a  common  wall  for 
both  cavities.  The  middle  ear  communicates  posteriorly  with  the  mastoid 
cells,  anteriorly  with  the  naso-pharynx  by  means  of  the  Eustachian  tube. 
The  interior  of  this  cavity  is  lined  by  mucous  membrane  continuous 
with  that  lining  the  pharynx. 

The  membrana  tympani  is  a  thin,  translucent,  nearly  circular  membrane, 
measuring  about  two-fifths  of  an  inch  in  diameter,  placed  at  the  inner  ter- 
mination of  the  external  auditory  canal.  The  membrane  is  enclosed  within 
a  ring  of  bone  which,  in  the  foetal  condition,  can  be  easily  removed,  but  in 
the  adult  condition  becomes  consolidated  with  the  surrounding  bone.  The 
membrana  tympani  consists  primarily  of  a  layer  of  fibrous  tissue,  arranged 
both  circularly  and  radially,  and  forms  the  membrana  propria  ;  externally, 
it  is  covered  by  a  thin  layer  of  skin  continuous  with  that  lining  the  auditory 
canal ;  internally,  it  is  covered  by  a  thin  mucous  membrane.  The  tympanic 
membrane  is  placed  obliquely  at  the  bottom  of  the  auditory  canal,  inclining 
at  an  angle  of  45°,  being  directed  from  behind  and  above  downward  and 
inward.  On  its  external  surface  this  membrane  presents  a  funnel-shaped 
depression,  the  sides  of  which  are  somewhat  convex. 

The  Ear-bones.  Running  across  the  tympanic  cavity  and  forming  an 
irregular  line  of  jointed  levers,  is  a  chain  of  bones  which  articulate  with 
each  other  at  their  extremities.  They  are  known  as  the  malleus,  incus  and 
stapes. 

The  form  and  position  of  these  bones  are  shown  in  Fig.  24. 

The  malleus  consists  of  a  head,  neck  and  handle,  of  which  the  latter  is 
attached  to  the  inner  surface  of  the  membrana  tympani ;  the  incus,  or  anvil 


THE   SENSE   OF    HEARING. 


167 


bone  presents  a  concave,  articular  surface,  which  receives  the  head  of  the 
malleus;  the  stapes,  or  stirrup  bone,  articulates  externally  with  the  long  pro- 
cess of  the  incus,  and  internally,  by  its  oval  base,  with  the  edges  of  the  fora- 
men ovale. 

The  tensor  tympani  muscle  consists  of  a  fleshy,  tapering  portion,  half 
an  inch  in  length,  which  terminates  in  a  slender  tendon ;  it  arises  from  the 


11 


TYMPANUM   AND   AUDITORY   OSSICLES   (LEFT)    MAGNIFIED. 

A.G.,  external  meatus  ;  M,  membrana  tympani,  which  is  attached  to  the  handle  of  the 
malleus,  n,  and  near  it  the  short  process,  /;  h,  head  of  the  malleus;  a,  incus  ;  k,  its 
short  process  with  its  ligament ;  /,  long  process ;  s,  Sylvian  ossicle ;  S,  stapes ;  A.X, 
A-r,  is  the  axis  of  rotation  of  the  ossicles ;  it  is  shown  in  perspective,  and  must  be 
imagined  to  penetrate  the  plane  of  the  paper  ;  t,  line  of  traction  of  the  tensor  tympani. 
The  other  arrows  indicate  the  movement  of  the  ossicles  when  the  tensor  contracts. 


cartilaginous  portion  of  the  Eustachian  tube  and  adjacent  surface  of  the 
sphenoid  bone.  From  this  origin  the  muscle  passes  nearly  horizontally 
backward  to  the  tympanic  cavity ;  just  opposite  to  the  fenestra  ovalis  its 
tendon  bends  at  a  right  angle  over  the  processus  cochleariformis  and  then 
passes  outward  across  the  cavity  to  be  inserted  into  the  handle  of  the  mal- 
leus near  the  neck. 


168  HUMAN   PHYSIOLOGY. 

The  stapedius  muscle  emerges  from  the  cavity  of  a  pyramid  of  bone 
projecting  from  the  posterior  wall  of  the  tympanum;  the  tendon  passes 
forward  and  is  inserted  into  the  neck  of  the  stapes  bone  posteriorly  near  its 
point  of  articulation  with  the  incus. 

The  laxator  tympani  muscle,  so-called,  is  now  generally  regarded  as  liga- 
mentous  in  nature,  and  not  muscular. 

The  Eustachian  tube,  by  means  of  which  a  free  communication  is 
established  between  the  middle  ear  and  pharynx,  is  partly  bony  and  partly 
cartilaginous  in  structure.  It  measures  about  an  inch  and  a  half  in  length ; 
commencing  at  its  opening  into  the  naso-pharynx  it  passes  upward  and  out- 
ward to  the  spine  of  the  sphenoid  bone,  at  which  point  it  becomes  some- 
what contracted ;  the  tube  then  dilates  as  it  passes  backward  into  the  middle 
ear  cavity ;  it  is  lined  by  mucous  membrane,  which  is  continued  into  the 
middle  ear  and  mastoid  cells. 

The  Function  of  the  Ear,  as  a  whole,  is  the  reception  and  transmis- 
sion of  aerial  vibrations  to  the  terminal  organs  concealed  within  the  in- 
ternal ear  and  which  are  connected  with  the  auditory  nerve  fibres.  The 
excitation  of  these  end  organs  caused  by  the  impact  of  the  vibrations, 
arouses  in  the  auditory  nerve  impulses  which  are  then  transmitted  to  the 
brain,  where  the  hearing  process  takes  place.  In  order  to  appreciate  the 
functions  of  the  individual  parts  of  the  ear  a  few  of  the  characteristics 
of  sound  waves  must  be  kept  in  mind. 

Sound  Waves.  All  sounds  are  caused  by  vibrations  in  the  atmosphere 
which  have  been  communicated  to  it  by  vibrating  elastic  bodies,  such  as 
membranes,  strings,  rods,  etc.  These  vibrating  bodies  produce  in  the  air 
a  to  and  fro  movement  of  its  particles,  resulting  in  a  series  of  alternate 
condensations  and  rarefactions  which  are  propagated  in  all  directions.  A 
complete  oscillation  of  a  particle  of  air  forward  and  backward  constitutes  a 
sound-wave.  Musical  sounds  are  caused  by  a  succession  of  regular  waves 
which  follow  each  other  with  a  certain  rapidity.  Noises  are  caused  by  the 
impact  of  a  series  of  irregular  waves. 

All  sound  waves  possess  intensity,  pitch,  and  quality.  The  intensity,  or 
loudness,  of  a  sound  depends  upon  the  amplitude  of  the  vibration,  or  the 
extent  of  its  excursion.  The//&v£  depends  upon  the  number  of  vibrations 
which  affect  the  auditory  nerve  in  a  second  of  time ;  the  pitch  of  the  note 
C,  the  first  below  the  leger  line  of  the  musical  scale,  is  caused  by  256 
vibrations  per  second  ;  the  pitch  of  the  same  note  an  octave  higher  is 
caused  by  512  vibrations  per  second.  If  the  vibrations  are  too  few  per 
second  they  fail  to  be  perceived  as  a  continuous  sound ;  the  minimum 


THE   SENSE   OF    HEARING.  109 

number  of  vibrations  capable  of  producing  a  sound  has  been  fixed  at  1 6  per 
second  ;  the  highest  pitched  musical  note  capable  of  being  heard  has  been 
shown  to  be  due  to  38,000  vibrations  per  second.  In  the  ascent  of  the 
musical  scale  there  is,  therefore,  a  gradual  increase  in  the  number  of  vibra- 
tions and  a  gradual  increase  in  the  pitch  of  the  sounds.  Between  the  two 
extreme  limits  lies  the  range  of  audibility,  which  embraces  eleven  octaves, 
of  which  seven  are  employed  in  the  musical  scale. 

The  quality  of  sound  depends  upon  a  combination  of  the  fundamental 
vibration  with  certain  secondary  vibrations  of  sub  divisions  of  the  vibrating 
body.  These  so-called  over-tones  vary  in  intensity  and  pitch,  and  by 
modifying  the  form  of  the  primary  wave  produce  that  which  is  termed 
the  quality  of  sound. 

Function  of  the  Pinna  and  External  Auditory  Canal.  In  those 
animals  possessing  movable  ears,  the  pinna  plays  an  important  part  in  the 
collection  of  sound-waves.  In  man,  in  whom  the  capability  of  moving  the 
pinna  has  been  lost,  it  is  doubtful  if  it  is  at  all  necessary  for  hearing.  Never- 
theless an  individual  with  dull  hearing  may  have  the  perception  of  sound 
increased  by  placing  the  pinna  at  an  angle  of  45°  to  the  side  of  the  head. 
The  external  auditory  canal  transmits  the  sonorous  vibrations  to  the  tym- 
panic membrane.  Owing  to  the  obliquity  of  this  canal  it  has  been  sup- 
posed that  the  waves,  concentrated  at  the  concha,  undergo  a  series  of  re- 
flections on  their  way  to  the  tympanic  membrane,  and,  owing  to  the 
position  of  this  membrane,  strike  it  almost  perpendicularly. 

Function  of  the  Tympanic  Membrane.  The  function  of  the  tym- 
panic membrane  appears  to  be  the  reception  of  sound  vibrations  by  being 
thrown  by  them  into  reciprocal  vibrations  which  correspond  in  intensity  and 
amplitude.  That  this  membrane  actually  reproduces  all  vibrations  within 
the  range  of  audibility  has  been  experimentally  demonstrated.  The  mem- 
brane not  being  fixed,  as  far  as  its  tension  is  concerned,  does  not  possess  a 
fixed  fundamental  note,  like  a  stationary  fixed  membrane,  and  is  therefore 
just  as  well  adapted  for  the  reception  of  one  set  of  vibrations  as  another. 
This  is  made  possible  by  variations  in  its  tension  in  accordance  with  the 
pitch  of  the  sounds.  In  the  absence  of  all  sound  the  membrane  is  in  a 
condition  of  relaxation  ;  with  the  advent  of  sound-waves  possessing  a 
gradual  increase  of  pitch,  as  in  the  ascent  of  the  musical  scale,  the  tension 
of  the  tympanic  membrane  is  gradually  increased  until  its  maximum  ten- 
sion is  reached  at  the  upper  limit  of  the  range  of  audibility.  By  this 
change  in  tension  certain  tones  become  perceptible  and  distinct,  while 
others  become  indistinct  and  inaudible. 

L 


170  HUMAN    PHYSIOLOGY. 

Function  of  the  Tensor  Tympani  Muscle.  The  function  of  this 
muscle  is,  as  its  name  indicates,  to  increase  the  tension  of  the  membrane  in 
accordance  with  the  pitch  of  the  sound  wave.  The  tendon  of  this  muscle 
playing  over  the  processus  cochleariformis  and  attached  at  almost  a  right 
angle  to  the  handle  of  the  malleus,  will,  when  the  muscle  contracts,  pull 
the  handle  inwards,  increase  the  convexity  of  the  membrane,  and  at  the 
same  time  increase  its  tension ;  with  the  relaxation  of  this  muscle,  the  handle 
of  the  malleus  passes  outward  and  the  tension  is  diminished.  The  contractions 
of  the  tensor  muscle  are  reflex  in  character  and  excited  by  nerve  impulses 
reaching  it  through  the  small  petrosal  nerve  and  otic  ganglion.  The  number 
of  nerve  stimuli  passing  to  the  muscle  and  determining  the  degree  of  con- 
traction will  depend  upon  the  pitch  of  the  Sound  wave  and  the  subsequent 
excitation  of  the  auditory  nerve.  The  tensor  tympani  muscle  may  be  re- 
garded as  an  accommodative  apparatus  by  which  the  tympanic  membrane  is 
adjusted  to  enable  it  to  receive  vibrations  of  varying  degrees  of  pitch. 

Function  of  the  Ossicles.  The  function  of  the  chain  of  bones  is  to 
transmit  the  sound  waves  across  the  tympanic  cavity  to  the  internal  ear. 
The  first  of  these  bones,  the  malleus,  being  attached  to  the  tympanic  mem- 
brane will  take  up  the  vibrations  much  more  readily  than  if  no  membrane 
intervened.  Owing  to  the  character  of  the  articulations,  when  the  handle 
of  the  malleus  is  drawn  inward,  the  position  of  the  bones  is  so  changed  that 
they  form  practically  a  solid  rod,  and  are  therefore  much  better  adapted  for  the 
transmission  of  molecular  vibrations  than  if  the  articulations  remained  loose. 
As  the  stapes  bone  is  somewhat  shorter  than  the  malleus,  its  vibrations  are 
smaller  than  those  of  the  tympanic  membrane,  and  by  this  arrangement  the 
amplitude  of  the  vibrations  is  diminished  but  their  force  increased. 

The  Function  of  the  Stapedius  Muscle  is,  according  to  Henle,  to 
fix  the  stapes  bone  so  as  to  prevent  too  great  a  movement  from  being  com- 
municated to  it  from  the  incus  and  transmitted  to  the  perilymph.  It  may 
be  looked  upon  therefore,  as  a  protective  muscle. 

The  Function  of  the  Eustachian  tube  is  to  maintain  a  free  communi- 
cation between  the  cavity  of  the  middle  ear  and  naso-pharynx.  The 
pressure  of  air  within  and  without  the  ear  is  thus  equalized,  and  the  vibra- 
tions of  the  tympanic  membrane  permitted  to  attain  their  maximum ;  one 
of  the  conditions  essential  for  the  reception  of  sound  waves.  The  impair- 
ment in  the  acuteness  of  hearing  which  is  caused  by  an  unequal  pressure  of 
the  air  in  the  middle  ear  can  be  shown :  I.  By  closing  the  mouth  and  nose 
and  forcing  air  from  the  lungs  through  the  Eustachian  tube  into  the  ear, 
producing  an  increase  in  pressure.  2.  By  closing  the  nose  and  mouth,  and 


THE   SENSE   OF   HEARING.  171 

making  efforts  at  deglutition,  which  withdraws  the  air  from  the  ear  and 
diminishes  its  pressure.  In  both  instances  the  free  vibrations  of  the 
tympanic  membrane  are  .interfered  with.  The  pharyngeal  orifice  of  the 
Eustachian  tube  is  opened  by  the  action  of  certain  of  the  muscles  of 
deglutition,  viz  :  the  levator  palati,  tensor  palati,  and  the  palato-pharyngei 
muscles. 

The  Internal  Ear,  or  Labyrinth,  is  located  in  the  petrous  portion  of 
the  temporal  bone,  and  consists  of  an  osseous  and  membranous  portion. 

The  Osseous  Labyrinth  is  divisible  into  three  parts,  viz :  the  vesti- 
bule, the  semicircular  canals  and  the  cochlea. 

The  vestibule  is  a  small,  triangular  cavity,  which  communicates  with  the 
middle  ear  by  the  foramen  ovale;  in  the  natural  condition  it  is  closed  by 
the  base  of  the  stapes  bone.  The  filaments  of  the  auditory  nerve  enter  the 
vestibule  through  small  foramina  in  the  inner  wall,  at  the  fovea  hemi- 
spherica. 

The  Semicircular  canals  are  three  in  number  ;  the  superior  vertical,  the 
inferior  vertical  and  the  horizontal,  each  of  which  opens  into  the  cavity  of 
the  vestibule  by  two  openings,  with  the  exception  of  the  two  vertical,  which 
at  one  extremity  open  by  a  common  orifice. 

The  Cochlea  forms  the  anterior  part  of  the  internal  ear.  It  is  a  gradually 
tapering  canal,  about  one  and  a  half  inches  in  length,  which  winds  spirally 
around  a  central  axis,  the  modiolus,  two  and  a  half  times.  The  interior  of 
the  cochlea  is  partly  divided  into  two  passages  by  a  thin  plate  of  bone,  the 
lamina  osseous  spiralis,  which  projects  from  the  central  axis  two-thirds 
across  the  canal.  These  passages  are  termed  the  scala  vestibuli  and  the 
scala  tympani,  from  their  communication  with  the  vestibule  and  tympanum. 
The  scala  tympani  communicates  with  the  middle  ear  through  fat  foramen 
rotundum,  which,  in  the  natural  condition,  is  closed  by  the  second  mem- 
brana  tympani ;  superiorly  they  are  united  by  an  opening,  the  helicotrema. 

The  whole  anterior  of  the  labyrinth,  the  vestibule,  the  semicircular 
canals,  and  the  scala  of  the  cochlea,  contains  a  clear,  limpid  fluid,  the  peri- 
lymph,  secreted  by  the  periosteum  lining  the  osseous  walls. 

The  Membranous  Labyrinth  corresponds  to  the  osseous  labyrinth 
with  respect  to  form,  though  somewhat  smaller  in  size. 

The  Vestibular  portion  consists  of  two  small  sacs,  the  titricle  and  saccule. 

The  Semicircular  canals  communicate  with  the  utricle  in  the  same 
manner  as  the  bony  canals  communicate  with  the  vestibule.  The  saccule 
communicates  with  the  membranous  cochlea  by  the  canalis  reuniens.  In 
the  interior  of  the  utricle  and  saccule,  at  the  entrance  of  the  auditory  nerve, 


172  HUMAN    PHYSIOLOGY. 

are  small  masses  of  carbonate  of  lime  crystals,  constituting  the  otoliths. 
Their  function  is  unknown. 

The  Membranous  cochlea  is  a  closed  tube,  commencing  by  a  blind 
extremity  at  the  first  turn  of  the  cochlea,  and  terminating  at  its  apex  by  a 
blind  extremity  also.  It  is  situated  between  the  edge  of  the  osseous  lamina 
spiralis  and  the  outer  wall  of  the  bony  cochlea,  and  follows  it  in  its  turns 
around  the  modiolus. 

A  transverse  section  of  the  cochlea  shows  that  it  is  divided  into  two 
portions  by  the  osseous  lamina  and  the  basilar  membrane:  I.  The  scala 
vestibuli,  bounded  by  the  periosteum  and  membrane  of  Reissner.  2.  The 
scala  tympani,  occupying  the  inferior  portion,  and  bounded  above  by  the 
septum,  composed  of  the  osseous  lamina  and  the  membrana  basilaris. 

The  true  membranous  canal  is  situated  between  the  membrane  of  Reiss- 
ner and  the  basilar  membrane.  It  is  triangular  in  shape,  but  is  partly 
divided  into  a  triangular  portion  and  a  quadrilateral  portion  by  the  tectorial 
membrane. 

The  Organ  of  Corti  is  situated  in  the  quadrilateral  portion  of  the  canal, 
and  consists  of  pillars  of  rods,  of  the  consistence  of  cartilage.  They  are 
arranged  in  two  rows ;  the  one  internal,  the  other  external ;  these  rods  rest 
upon  the  basilar  membrane;  their  bases  are  separated  from  each  other,  but 
their  upper  extremities  are  united,  forming  an  arcade.  In  the  internal  row 
it  is  estimated  there  are  about  3500,  and  in  the  external  row  about  5200  of 
these  rods. 

On  the  inner  side  of  the  internal  row  is  a  single  layer  of  elongated  hair 
cells ;  on  the  outer  surface  of  the  external  row  are  three  such  layers  of  hair 
cells.  Nothing  definite  is  known  as  to  their  function. 

The  Endolymph  occupies  the  interior  of  the  utricle,  saccule,  membranous 
canals,  and  bathes  the  strictures  in  the  interior  of  the  membranous  cochlea, 
throughout  its  entire  extent. 

The  Auditory  Nerve  at  the  bottom  of  the  internal  auditory  meatus 
divides  into  (l)  a  vestibular  branch,  which  is  distributed  to  the  utricle  and 
semicircular  canals ;  (2)  a  cochlear  branch,  which  passes  into  the  central 
axis  at  its  base,  and  ascends  to  its  apex ;  as  it  ascends,  fibres  are  given  off, 
which  pass  between  the  plates  of  the  osseous  lamina,  to  be  ultimately  con- 
nected with  the  organ  of  Corti. 

The  Function  of  the  semicircular  canals  appears  to  be  to  assist  in  main- 
taining the  equilibrium  of  the  body ;  destruction  of  the  vertical  canal  is 
followed  by  an  oscillation  of  the  head  upward  and  downward ;  destruction 
of  the  horizontal  canal  is  followed  by  oscillations  from  left  to  right.  When 


VOICE   AND   SPEECH.  173 

the  canals  are  injured  on  both  sides,  the  animal  loses  the  power  of  main- 
taining equilibrium  upon  making  muscular  movements. 

Function  of  the  Cochlea.  It  is  regarded  as  possessing  the  power  of 
appreciating  the  quality  of  pitch  and  the  shades  of  different  musical  tones. 
The  elements  of  the  organ  of  Corti  are  analogous,  in  some  respects,  to  a 
musical  instrument,  and  are  supposed,  by  Helmholtz,  to  be  tuned  so  as  to 
vibrate  in  unison  with  the  different  tones  conveyed  to  the  internal  ear. 

Summary.  The  waves  of  sound  are  gathered  together  by  the  pinna 
and  external  auditory  meatus,  and  conveyed  to  the  membrana  tympani. 
This  membrane,  made  tense  or  lax  by  the  action  of  the  tensor  tympani 
and  laxator  tympani  muscles,  is  enabled  to  receive  sound  waves  of  either 
a  high  or  low  pitch.  The  vibrations  are  conducted  across  the  middle  ear 
by  a  chain  of  bones  to  the  foramen  ovale,  and  by  the  column  of  air  of 
the  tympanum  to  the  foramen  rotundum,  which  is  closed  by  the  second 
membrana  tympani;  the  pressure  of  the  air  in  the  tympanum  being  regu- 
lated by  the  Eustachian  tube. 

The  internal  ear  finally  receives  the  vibrations,  which  excite  vibrations 
successively  in  the  perilymph,  the  walls  of  the  membranous  labyrinth,  the 
endolymph,  and,  lastly,  the  terminal  filaments  of  the  auditory  nerve,  by 
which  they  are  conveyed  to  the  brain. 


VOICE  AND  SPEECH. 

The  Larynx  is  the  organ  of  voice.  Speech  is  a  modification  of  voice, 
and  is  produced  by  the  teeth  and  the  muscles  of  the  lips  and  tongue,  co- 
ordinated in  their  action  by  stimuli  derived  from  the  cerebrum. 

The  Structures  entering  into  the  formation  of  the  larynx  are  mainly 
the  thyroid,  cricoid  and  arytenoid  cartilages ;  they  are  so  situated  and 
united  by  means  of  ligaments  and  muscles  as  to  form  a  firm  cartilaginous 
box.  The  larynx  is  covered  externally  by  fibrous  tissue,  and  lined  inter- 
nally with  mucous  membrane. 

The  Vocal  Cords  are  four  ligamentous  bands,  running  antero-posteri- 
orly  across  the  upper  portion  of  the  larynx,  and  are  divided  into  the  two 
superior  or  false  vocal  cords,  and  the  two  inferior  or  true  vocal  cords ; 
they  are  attached  anteriorly  to  the  receding  angle  of  the  thyroid  cartilages 
and  posteriorly  to  the  anterior  part  of  the  base  of  the  arytenoid  cartilages. 
The  space  between  the  true  vocal  cords  is  the  rinia  glottidis. 

The  Muscles  which  have  a  direct  action  upon  the  movements  of  the 


174  HUMAN   PHYSIOLOGY. 

vocal  cords  are  nine  in  number,  and  take  their  names  from  their  points  of 
origin  and  insertion,  viz :  the  two  crico-thyroid,  two  thyro-arytenoid,  two 
posterior  crico-arytenoid,  two  lateral  crico-arytenoid,  and  one  arytenoid 
muscles. 

The  crico-thyroid  muscles,  by  their  contraction,  render  the  vocal  cords 
more  tense  by  drawing  down  the  anterior  portion  of  the  thyroid  cartilage 
and  approximating  it  to  the  cricoid,  and  at  the  same  time  tilting  the  pos- 
terior portion  of  the  cricoid  and  arytenoid  cartilages  backward. 

The  thyro-arytenoid,  by  their  contraction,  relax  the  vocal  cords  by  draw- 
ing the  arytenoid  cartilage  forward  and  the  thyroid  backward. 

The  posterior  crico-arytenoid  muscles,  by  their  contraction,  rotate  the 
arytenoid  cartilages  outward  and  thus  separate  the  vocal  cords  and  enlarge 
the  aperture  of  the  glottis.  They  principally  aid  the  respiratory  movements 
during  inspiration. 

The  lateral  crico-arytenoid  muscles  are  antagonistic  to  the  former,  and 
by  their  contraction  rotate  the  arytenoid  cartilages  so  as  to  approximate  the 
vocal  cords  and  constrict  the  glottis. 

The  arytenoid  muscle  assists  in  the  closure  of  the  aperture  of  the  glottis. 

The  inferior  laryngeal  nerve  animates  all  the  muscles  of  the  larynx,  with 
the  exception  of  the  crico  thyroid. 

Movements  of  the  Vocal  Cords.  During  respiration  the  move- 
ments of  the  vocal  cords  differ  from  those  occurring  during  the  production 
of  voice. 

At  each  inspiration,  the  true  vocal  cords  are  widely  separated,  and  the 
aperture  of  the  glottis  is  enlarged  by  the  action  of  the  crico-arytenoid 
muscles,  which  rotate  outward  the  anterior  angle  of  the  base  of  the  aryte- 
noid cartilages;  at  each  expiration  the  larynx  becomes  passive;  the 
elasticity  of  the  vocal  cords  returns  them  to  their  original  position,  and  the 
air  is  forced  out  by  the  elasticity  of  the  lungs  and  the  walls  of  the  thorax. 

Phonation.  As  soon  as  phonation  is  about  to  be  accomplished  a  marked 
change  in  the  glottis  is  noticed  with  the  aid  of  the  laryngoscope.  The 
true  vocal  cords  suddenly  become  approximated  and  are  made  parallel, 
giving  to  the  glottis  the  appearance  of  a  narrow  slit,  the  edges  of  which  are 
capable  of  vibrating  accurately  and  rapidly;  at  the  same  time  their  tension 
is  much  increased. 

With  the  vocal  cords  thus  prepared,  the  expiratory  muscles  force  the 
column  of  air  into  the  lungs  and  trachea  through  the  glottis,  throwing  the 
edges  of  the  cords  into  vibration. 

The //A:/;  of  sounds  depends  upon  the  extent  to  which  the  vocal  cords 
are  made  tense  and  the  length  of  the  aperture  through  which  the  air  passes. 


VOICE   AND   SPEECH.  175 

In  the  production  of  sounds  of  a  high  pitch  the  tension  of  the  vocal  cords 
becomes  very  marked,  and  the  glottis  diminished  in  length.  When  grave 
sounds,  having  a  low  pitch,  are  omitted  from  the  larynx,  the  vocal  cords 
are  less  tense  and  their  vibrations  are  large  and  loose. 

The  quality  of  voice  depends  upon  the  length,  size  and  thickness  of  the 
cords,  and  the  size,  form  and  construction  of  the  trachea,  larynx  and  the 
resonant  cavities  of  the  pharynx,  nose  and  mouth. 

The  compass  of  the  voice  comprehends  from  two  to  three  octaves.  The 
range  is  different  in  the  two  sexes ;  the  lowest  note  of  the  male  being  about 
one  octave  lower  than  the  lowest  note  of  the  female  :  while  the  highest 
note  of  the  male  is  an  octave  less  than  the  highest  note  of  the  female. 

The  varieties  of  voices,  e.g.,  bass,  baritone,  tenor,  contralto,  mezzo- 
soprano  and  soprano,  are  due  to  the  length  of  the  vocal  cords ;  being 
longer  when  the  voice  has  a  low  pitch,  and  shorter  when  it  has  a  high  pitch. 

Speech  is  the  faculty  of  expressing  ideas  by  means  of  combinations  of 
sounds,  in  obedience  to  the  dictates  of  the  cerebrum. 

Articulate  sozinds  may  be  divided  into  vcnvels  and  consonants.  The 
vowel  sounds,  a,  e,  i,  o,  u,  are  produced  in  the  larynx  by  the  vocal  cords. 
The  consonantal  sounds  are  produced  in  the  air  passages  above  the  larynx 
by  an  interruption  of  the  current  of  air  by  the  lips,  tongue  and  teeth ;  the 
consonants  may  be  divided  into:  (i)  mutes,  b,  d,  /£,/,  t,  c,g;  (2)  dentals, 
</,/,  s,  /,  z;  (3  )nasals,  m,  n,  ng  ;  (4)  labials,  £,/,/,  v,  m  ;  (5)  gutturals, 
k,  g,  c,  and  g  hard  /  (6)  liquids,  /,  ///,  n,  r. 


176  HUMAN   PHYSIOLOGY. 


REPRODUCTION. 

Reproduction  is  the  function  by  which  the  species  is  preserved,  and 
accomplished  by  the  organs  of  generation  in  the  two  sexes. 


GENERATIVE  ORGANS  OF  THE  FEMALE. 

The  Generative  Organs  of  the  Female  consist  of  the  ovaries,  Fallo- 
pian tubes,  uterus  and  vagina. 

The  Ovaries  are  two  small,  ovoid,  flattened  bodies,  measuring  one  inch 
and  a  half  in  length  and  three-quarters  of  an  inch  in  width;  they  are  situ- 
ated in  the  cavity  of  the  pelvis,  and  imbedded  in  the  posterior  layer  of  the 
broad  ligament;  attached  to  the  uterus  by  a  round  ligament,  and  to  the  ex- 
tremities of  the  Fallopian  tubes  by  the  fimbrke.  The  ovary  consists  of  an 
external  membrane  of  fibrous  tissue,  the  cortical  portion,  in  which  are  im- 
bedded the  Graafian  vesicles,  and  an  internal  portion,  the  stroma,  contain- 
ing blood  vessels. 

The  Graafian  Vesicles  are  exceedingly  numerous,  but  situated  only  in 
the  cortical  portion.  Although  the  ovary  contains  the  vesicles  from  the 
period  of  birth,  it  is  only  at  the  period  of  puberty  that  they  attain  their  full 
development.  From  this  time  onward  to  the  catamenial  period,  there  is  a 
constant  growth  and  maturation  of  the  Graafian  vesicles.  They  consist  of 
an  external  investment,  composed  of  fibrous  tissue  and  blood  vessels,  in  the 
interior  of  which  is  a  layer  of  cells  forming  the  membrana  granulosa  ;  at 
its  lower  portion  there  is  an  accumulation  of  cells,  the  proligerous  disc,  in 
which  the  ovum  is  contained.  The  cavity  of  the  vesicle  contains  a  slightly 
yellowish,  alkaline,  albuminous  fluid. 

The  Ovum  is  a  globular  body,  measuring  about  the  T|5  of  an  inch  in 
diameter;  it  consists  of  an  external  investing  membrane,  the  vitelline  mem- 
brane, a  central  granular  substance,  the  vitellus  or  yelk,  a  nucleus,  the 
germinal  vesicle,  in  the  interior  of  which  is  imbedded  the  nucleolus,  or 
germinal  spot. 

The  Fallopian  Tubes  are  about  four  inches  in  length,  and  extend  out- 
ward from  the  upper  angles  of  the  uterus,  between  the  folds  of  the  broad 
ligaments,  and  terminate  in  a  fringed  extremity,  which  is  attached  by  one  of 
the  fringes  to  the  ovary.  They  consist  of  three  coats  :  (i)  the  external,  or 


GENERATIVE   ORGANS    OF   THE   FEMALE.  177 

peritoneal,  (2)  middle,  or  muscular,  the  fibres  of  which  are  arranged  in  a 
circular  or  longitudinal  direction,  (3)  internal,  or  mucous,  covered  with 
ciliated  epithelial  cells,  which  are  always  waving  from  the  ovary  toward 
the  uterus. 

The  Uterus  is  pyriform  in  shape,  and  may  be  divided  into  a  body  and 
neck ;  it  measures  about  three  inches  in  length  and  two  inches  in  breadth 
in  the  unimpregnated  state.  At  the  lower  extremity  of  the  neck  is  the  os 
externum ;  at  the  junction  of  the  neck  with  the  body  is  a  constriction,  the 
os  internum.  The  cavity  of  the  uterus  is  triangular  in  shape,  the  walls  of 
which  are  almost  in  contact. 

The  walls  of  the  uterus  are  made  up  of  several  layers  of  non-striated 
muscular  fibres,  covered  externally  by  peritoneum,  and  lined  internally  by 
mucous  membrane,  containing  numerous  tubular  glands,  and  covered  by 
ciliated  epithelial  cells. 

The  Vagina  is  a  membranous  canal,  from  five  to  six  inches  in  length, 
situated  between  the  rectum  and  bladder.  It  extends  obliquely  upward 
from  the  surface,  almost  to  the  brim  of  the  pelvis,  and  embraces  at  its  upper 
extremity  the  neck  of  the  uterus. 

Discharge  of  the  Ovum.  As  the  Graafian  vesicle  matures,  it  increases 
in  size,  from  an  augmentation  of  its  liquid  contents,  and  approaches  the 
surface  of  the  ovary,  where  it  forms  a  projection,  measuring  from  one-fourth 
to  one-half  an  inch  in  size.  The  maturation  of  the  vesicle  occurs  periodically, 
about  every  twenty-eight  days,  and  is  attended  by  the  phenomena  of  men- 
struation. During  this  period  of  active  congestion  of  the  reproductive 
organs,  the  Graafian  vesicle  ruptures,  the  ovum  and  liquid  contents  escape, 
and  are  caught  by  the  fimbriated  extremity  of  the  Fallopian  tube,  which 
has  adapted  itself  to  the  posterior  surface  of  the  ovary.  The  passage  of 
the  ovum  through  the  Fallopian  tube  into  the  uterus  occupies  from  ten  to 
fourteen  days,  and  is  accomplished  by  muscular  contraction  and  the  action 
of  the  ciliated  epithelium. 

Menstruation  is  a  periodical  discharge  of  blood  from  the  mucous  mem- 
brane of  the  uterus,  due  to  a  fatty  degeneration  of  the  small  blood  vessels. 
Under  the  pressure  of  an  increased  amount  of  blood  in  the  reproductive 
organs,  attending  the  process  of  ovulation,  the  blood  vessels  rupture,  and  a 
hemorrhage  takes  place  into  the  uterine  cavity;  thence  it  passes  into  the 
vagina.  Menstruation  lasts  from  five  to  six  days,  and  the  amount  of  blood 
discharged  averages  about  five  ounces. 

Corpus  Luteum.  For  some  time  anterior  to  the  rupture  of  a  Graafian 
vesicle,  it  increases  in  size  and  becomes  vascular;  its  walls  become  thick- 


178 


HUMAN    PHYSIOLOGY. 


ened,  from  the  deposition  of  a  reddish-yellow,  glutinous  substance,  a 
product  of  cell  growth  from  the  proper  coat  of  the  follicle  and  the  membrana 
granulosa.  After  the  ovum  escapes,  there  is  usually  a  small  effusion  of 
blood  into  the  cavity  of  the  follicle,  which  soon  coagulates,  loses  its  coloring 
matter,  and  acquires  the  characteristics  of  fibrin,  but  it  takes  no  part  in  the 
formation  of  the  corpus  luteum.  The  walls  of  the  follicle  become  convo- 
luted, vascular,  and  undergo  hypertrophy,  until  they  occupy  the  whole  of 
the  follicular  cavity.  At  its  period  of  fullest  development,  the  corpus  luteum 
measures  three-fourths  of  an  inch  in  length  and  half  an  inch  in  depth.  In 
a  few  weeks  the  mass  loses  its  red  color,  and  becomes  yellow,  constituting 
the  corpus  luteum  or  yellow  body.  It  then  begins  to  retract,  and  becomes 
pale;  and  at  the  end  of  two  months  nothing  remains  but  a  small  cicatrix 
upon  the  surface  of  the  ovary.  Such  are  the  changes  in  the  follicle,  if  the 
ovum  has  not  been  impregnated. 

The  corpus  luteum,  after  impregnation  has  taken  place,  undergoes  a 
much  slower  development,  becomes  larger,  and  continues  during  the  entire 
period  of  gestation.  The  difference  between  the  corpus  luteum  of  the 
unimpregnated  and  pregnant  condition  is  expressed  in  the  following  table 
by  Dalton : — 


Corpus  Luteum  of  Menstruation.      Corpus  Luteum  of  Pregnancy. 


At   the    end  of 

three  weeks. 
One  month. 


Two  months. 


Four  months. 


Six  months. 


Nine  months. 


Three-quarters  of    an  inch  in 
reddish  ;  convoluted  wall  pale. 


diameter;  central  clot 


Smaller ;  convoluted 
wall  bright  yellow  ;  clot 
still  reddish. 

Reduced  to  the  condi- 
tion of  an  insignificant 
cicatrix. 

Absent  or  unnoticeable. 


Absent. 


Absent. 


Larger  ;  convoluted  wall 
bright  yellow  ;  clot  still  red- 
dish. 

Seven-eighths  of  an  inch 
in  diameter;  convoluted  wall 
bright  yellow;  clot  perfectly 
decolorized. 

Seven- eighths  of  an  inch 
in  diameter;  clot  pale  and 
fibrinous ;  convoluted  wall 
dull  yellow. 

Still  as  large  as  at  the  end 
of  second  month  ;  clot  fibrin- 
ous ;  convoluted  wall  paler. 

Half  an  inch  in  diameter; 
central  clot  converted  into  a 
radiating  cicatrix  ;  external 
wall  tolerably  thick  and  con- 
voluted, but  without  any 
bright  yellow  color. 


GENERATIVE  ORGANS  OF  THE  MALE.  179 

GENERATIVE  ORGANS  OF  THE  MALE. 

The  Generative  Organs  of  the  Male  consist  of  the  testicles,  vasa 
deferentia,  vesiculse  seminales  and  penis. 

The  Testicles,  the  essential  organs  of  reproduction  in  the  male,  are 
two  oblong  glands,  about  an  inch  and  a  half  in  length,  compressed  from 
side  to  side,  and  situated  in  the  cavity  of  the  scrotum. 

The  proper  coat  of  the  testicle,  the  tunica  albuginea,  is  a  white,  fibrous 
structure,  about  the  -fa  of  an  inch  in  thickness ;  after  enveloping  the  testicle, 
it  is  reflected  into  its  interior  at  the  posterior  border,  and  forms  a  vertical 
process,  the  mediastinum  testes,  from  which  septa  are  given  off,  dividing 
the  testicle  in  lobules. 

The  substance  of  the  testicle  is  made  up  of  the  seminiferous  tubules, 
which  exist  to  the  number  of  840;  they  are  exceedingly  convoluted,  and 
when  unraveled  are  about  30  inches  in  length.  As  they  pass  toward  the 
apices  of  the  lobules  they  become  less  convoluted,  and  terminate  in  from 
20  to  30  straight  ducts,  the  vasa  rectay  which  pass  upward  through  the 
mediastinum  and  constitute  the  rete  teslis.  At  the  upper  part  of  the 
mediastinum  the  tubules  unite  to  form  from  9  to  30  small  ducts,  the  vasa 
efferentia,  which  become  convoluted,  and  form  the  globus  major  of  the 
epididymis ;  the  continuation  of  the  tubes  downward  behind  the  testicle 
and  a  second  convolution  constitutes  the  body  and  globus  minor. 

The  seminal  tubule  consists  of  a  basement  membrane  lined  by  granular 
nucleated  epithelium. 

The  Vas  Deferens,  the  excretory  duct  of  the  testicle,  is  about  two  feet 
in  length,  and  may  be  traced  upward  from  the  epididymis  to  the  under  sur- 
face of  the  base  of  the  bladder,  where  it  unites  with  the  duct  of  the  vesicula 
seminalis,  to  form  the  ejaculatory  duct. 

The  Vesiculae  Seminales  are  two  lobulated,  pyriform  bodies,  about 
two  inches  in  length,  situated  on  the  under  surface  of  the  bladder. 

They  have  an  external  fibrous  coat,  a  middle  muscular  coat,  and  an 
internal  mucous  coat,  covered  by  epithelium,  which  secretes  a  mucous  fluid. 
The  vesiculse  seminales  serve  as  reservoirs,  in  which  the  seminal  fluid  is 
temporarily  stored  up. 

The  Ejaculatory  Duct,  about  y£  °f  an  mcn  m  length,  opens  into  the 
urethra,  and  is  formed  by  the  union  of  the  vasa  deferentia  and  the  ducts  of 
the  vesicube  seminales. 

The  Prostate  Gland  surrounds  the  posterior  extremity  of  the  urethra, 
and  opens  into  it  by  from  twenty  to  thirty  openings,  the  orifices 


180  HUMAN    PHYSIOLOGY. 

tatic  tubules.  The  gland  secretes  a  fluid  which  forms  part  of  the  semen, 
and  assists  in  maintaining  the  vitality  of  the  spermatozoa. 

Semen  is  a  complex  fluid,  made  up  of  the  secretions  from  the  testicles, 
the  vesiculae  seminales,  the  prostatic  and  urethral  glands.  It  is  grayish- 
white  in  color,  mucilaginous  in  consistence,  of  a  characteristic  odor,  and 
somewhat  heavier  than  water.  From  half  a  drachm  to  a  drachm  is  ejacu- 
lated at  each  orgasm. 

The  Spermatozoa  are  peculiar  anatomical  elements,  developed  within 
the  seminal  tubules,  and  possess  the  power  of  spontaneous  movement. 
The  spermatozoa  consist  of  a  conoidal  head  and  a  long  filamentous  tail, 
which  is  in  continuous  and  active  motion;  as  long  as  they  remain  in  the 
vas  deferens  they  are  quiescent,  but  when  free  to  move  in  the  fluid  of  the 
vesicuke  seminales,  become  very  active. 

Origin.  The  spermatozoa  appear  at  the  age  of  puberty,  and  are  then 
constantly  formed  until  an  advanced  age.  They  are  developed  from  the 
nuclei  of  large,  round  cells  contained  in  the  anterior  of  the  seminal  tubules, 
as  many  as  fifteen  to  twenty  developing  in  a  single  cell. 

When  the  spermatozoa  are  introduced  into  the  vagina,  they  pass  readily 
into  the  uterus  and  through  the  Fallopian  tubes  toward  the  ovaries,  where 
they  remain  and  retain  their  vitality  for  a  period  of  from  8  to  10  days. 

Fecundation  is  the  union  of  the  spermatozoa  with  the  ovum  during  its 
passage  toward  the  uterus,  and  usually  takes  place  in  the  Fallopian  tube, 
just  outside  of  the  womb.  After  floating  around  the  ovum  in  an  active  man- 
ner, they  penetrate  the  vitelline  membrane,  pass  into  the  interior  of  the 
vitellus,  where  they  lose  their  vitality,  and  along  with  the  germinal  vesicle 
entirely  disappear. 


DEVELOPMENT  OF  ACCESSORY  STRUCTURES. 

Segmentation  of  the  Vitellus.  After  the  disappearance  of  the 
spermatozoa  and  the  germinal  vesicle  there  remains  a  transparent,  granular, 
albuminous  substance,  in  the  centre  of  which  a  new  nucleus  soon  appears; 
this  constitutes  the  parent  cells,  and  is  the  first  stage  in  the  development  of 
the  new  being. 

Following  this,  the  vitellus  undergoes  segmentation;  a  constriction 
appears  on  the  opposite  side  of  the  vitellus,  which  gradually  deepens, 
until  the  yelk  is  divided  into  two  segments,  each  of  which  has  a  distinct 
nucleus  and  nucleolus;  these  two  segments  undergo  a  further-  division  into 
four,  the  four  into  eight,  the  eight  into  others,  and  so  on,  until  the  entire 


DEVELOPMENT   OF  ACCESSORY    STRUCTURES.  181 

vitellas  is  divided  into  a  great  number  of  cells,  each  of  which  contains  a 
nucleus  and  nucleolus. 

The  peripheral  cells  of  this  "  mulberry  mass  "  then  arrange  themselves 
so  as  to  form  a  membrane,  and  as  they  are  subjected  to  mutual  pressure, 
assume  a  polyhedral  shape,  which  gives  to  the  membrane  a  mosaic  appear- 
ance. The  central  part  of  the  vitellus  becomes  filled  with  a  clear  fluid. 
A  secondary  membrane  shortly  appears  within  the  first,  and  the  two  together 
constitute  the  external  and  internal  blasted ermic  membranes. 

Germinal  Area.  At  about  this  period  there  is  an  accumulation  of 
cells  at  a  certain  spot  upon  the  surface  of  the  blastodermic  membranes 
which  marks  the  position  of  the  future  embryo.  This  spot,  at  first  circular, 
soon  becomes  elongated,  and  forms  the  primitive  trace,  around  which  is  a 
clear  space,  the  area  pellucida,  which  is  itself  surrounded  by  a  darker  region, 
the  area  opaca. 

The  primitive  trace  soon  disappears,  and  the  area  pellucida  becomes 
guitar-shaped;  a  new  groove,  the  medullary  groove,  is  now  formed,  which 
develops  from  before  backward,  and  becomes  the  neural  canal. 

Blastodermic  Membranes.  The  embryo,  at  this  period,  consists  of 
three  layers,  viz. :  the  external  and  internal  blastodermic  membranes,  and  a 
middle  membrane  formed  by  a  genesis  of  cells  from  their  internal  surfaces. 
These  layers  are  known  as  the  epiblast,  mesoblast  and  hypoblast. 

The  Epiblast  gives  rise  to  the  central  nervous  system,  the  epidermis  of 
the  skin  and  its  appendages,  and  the  primitive  kidneys. 

The  Mesoblast  gives  rise  to  the  dermis,  muscles,  bones,  nerves,  blood 
vessels,  sympathetic  nervous  system,  connective  tissue,  the  urinary  and 
reproductive  apparatus  and  the  walls  of  the  alimentary  canal. 

The  Hypoblast  gives  rise  to  the  epithelial  lining  of  the  alimentary  canal 
and  its  glandular  appendages,  the  liver  and  pancreas,  and  the  epithelium 
of  the  respiratory  tract. 

Dorsal  Laminae.  As  development  advances,  the  true  medullary 
groove  deepens,  and  there  arise  two  longitudinal  elevations  of  the  epiblast, 
the  dorsal  lamina;,  one  on  either  side  of  the  groove,  which  grow  up,  arch 
over  and  unite  so  as  to  form  a  closed  tube,  the  primitive  central  nervous 
system. 

The  Chorda  Dorsalis  is  a  cylindrical  rod  running  almost  throughout 
the  entire  length  of  the  embryo.  It  is  formed  by  an  aggregation  of  meso- 
blastic  cells,  and  situated  immediately  beneath  the  medullary  groove. 

Primitive  Vertebras.  On  either  side  of  the  neural  canal  the  cells 
of  the  mesoblast  undergo  a  longitudinal  thickening,  which  develops  and 


182  HUMAN   PHYSIOLOGY. 

extends  around  the  neural  canal  and  the  chorda  dorsalis,  and  forms  the 
arches  and  bodies  of  the  vertebrae.  They  become  divided  transversely  into 
four-sided  segments. 

The  Mesoblast  now  separates  into  two  layers ;  the  external,  joining  with 
the  epiblast,  forms  the  somalopleure ;  the  internal,  joining  with  the  hypo- 
blast,  forms  the  splanchnopleure ;  the  space  between  them  constituting  the 
pleuro-peritoneal  cavity. 

Visceral  Laminae.  The  walls  of  the  pleuro-peritoneal  cavity  are 
formed  by  a  downward  prolongation  of  the  somatopleure  (the  visceral 
lamince],  which,  as  they  extend  around  in  front,  pinch  off  a  portion  of  the 
yelk  sac  (formed  by  the  splanchnopleure),  which  becomes  the  primitive 
alimentary  canal ;  the  lower  portion,  remaining  outside  of  the  body  cavity, 
forms  the  timbilical  vesicle,  which  after  a  time  disappears. 

Formation  of  Foetal  Membranes.  The  Amnion  appears  shortly 
after  the  embyro  begins  to  develop,  and  is  formed  by  folds  of  the  epiblast 
and  external  layer  of  the  mesoblast,  rising  up  in  front  and  behind,  and  on 
each  side ;  these  amniotic  folds  gradually  extend  over  the  back  of  the 
embryo  to  a  certain  point,  where  they  coalesce,  and  enclose  a  cavity,  the 
amniotic  cavity.  The  membranous  partition  between  the  folds  disappears, 
and  the  outer  layer  recedes  and  becomes  blended  with  the  vitelline  mem- 
brane, constituting  the  chorion,  the  external  covering  of  the  embryo. 

The  Allantois.  As  the  amnion  develops,  there  grows  out  from  the 
posterior  portion  of  the  alimentary  canal  a  pouch,  or  diverticulum,  the 
allantois,  which  carries  blood  vessels  derived  from  the  intestinal  circulation. 
As  it  gradually  enlarges,  it  becomes  more  vascular,  and  inserts  itself  be- 
tween the  two  layers  of  the  amnion,  coming  into  intimate  contact  with  the 
external  layer.  Finally,  from  increased  growth,  it  completely  surrounds 
the  embryo,  and  its  edges  become  fused  together. 

In  the  bird,  the  allantois  is  a  respiratory  organ,  absorbing  oxygen  and 
exhaling  carbonic  acid ;  it  also  absorbs  nutritious  matter  from  the  interior 
of  the  egg. 

Amniotic  Fluid.  The  amnion,  when  first  formed,  is  in  close  contact 
with  the  surface  of  the  ovum ;  but  it  soon  enlarges,  and  becomes  filled 
with  a  clear,  transparent  fluid,  containing  albumin,  glucose,  fatty  matters, 
urea  and  inorganic  salts.  It  increases  in  amount  up  to  the  latter  period  of 
gestation,  when  it  amounts  to  about  two  pints.  In  the  space  between  the 
amnion  and  allantois  is  a  gelatinous  material,  which  is  encroached  upon, 
and  finally  disappears  as  the  amnion  and  allantois  come  in  contact,  at  about, 
the  fifth  month. 


DEVELOPMENT  OF  ACCESSORY  STRUCTURES.  183 

The  Chorion,  the  external  investment  of  the  embryo,  is  formed  by  a 
fusion  of  the  original  vitelline  membrane,  the  external  layer  of  the  amnion, 
and  the  allantois.  The  external  surface  now  becomes  covered  with  villous 
processes,  which  increase  in  number  and  size  by  the  continual  budding 
and  growth  of  club-shaped  processes  from  the  main  stem,  and  give  to  the 
chorion  a  shaggy  appearance.  They  consist  of  a  homogeneous  granular 
matter,  and  are  penetrated  by  branches  of  the  blood  vessels  derived  from 
the  aorta. 

The  presence  of  villous  processes  in  the  uterine  cavity  is  proof  positive 
of  the  previous  existence  of  a  foetus.  They  are  characteristic  of  the 
chorion,  and  are  found  under  no  other  circumstances. 

At  about  the  end  of  the  second  month  the  villosities  begin  to  atrophy 
and  disappear  from  the  surface  of  the  chorion,  with  the  exception  of  those 
situated  at  the  points  of  entrance  of  the  foetal  blood  vessels,  which  occupy 
about  one-third  of  its  surface,  where  they  continue  to  grow  longer,  become 
more  vascular,  and  ultimately  assist  in  the  formation  of  the  placenta ;  the 
remaining  two- thirds  of  the  surface  loses  its  villi  and  blood  vessels,  and 
becomes  a  simple  membrane. 

The  Umbilical  Cord  connects  the  foetus  with  that  portion  of  the 
chorion  which  forms  the  fcetal  side  of  the  placenta.  It  is  a  process  of  the 
allantois,  and  contains  two  arteries  and  a  vein,  which  have  a  more  or  less 
spiral  direction.  It  appears  at  the  end  of  the  first  month,  and  gradually 
increases  in  length,  until,  at  the  end  of  gestation,  it  measures  about  twenty 
inches.  The  cord  is  also  surrounded  by  a  process  of  the  amnion. 

Development  of  the  Decidual  Membrane.  The  interior  of  the 
uterus  is  lined  by  a  thin,  delicate  mucous  membrane,  in  which  are  im 
bedded  immense  numbers  of  tubules,  terminating  in  blind  extremities,  the 
uterine  tubules.  At  each  period  of  menstruation  the  mucous  membrane 
becomes  thickened  and  vascular,  which  condition,  however,  disappears 
after  the  usual  menstrual  discharge.  When  the  ovum  becomes  fecundated, 
the  mucous  membrane  takes  on  an  increased  growth,  becomes  more  hyper- 
trophied  and  vascular,  sends  up  little  processes,  or  elevations  from  its  sur- 
face, and  constitutes  the  decidua  vera. 

As  the  ovum  passes  from  the  Fallopian  tube  into  the  interior  of  the 
uterus,  the  primitive  vitelline  membrane,  covered  with  villosities,  becomes 
entangled  with  the  processes  of  the  mucous  membrane.  A  portion  of  the 
decidua  vera  then  grows  up  on  all  sides,  and  encloses  the  ovum,  forming 
the  decidua  reflexa,  while  the  villous  processes  of  the  chorion  insert  them- 
selves into  the  uterine  tubules,  and  in  the  mucous  membrane  between 
them. 


184  HUMAN    PHYSIOLOGY.' 

As  development  advances  the  decidua  reflexa  increases  in  size,  and  at 
about  the  end  of  the  fourth  month  comes  in  contact  with  the  decidua  vera, 
with  which  it  is  ultimately  fused. 

The  Placenta.  Of  all  the  embryonic  structures,  the  placenta  is  the 
most  important.  It  is  formed  in  the  third  month,  and  then  increases  in  size 
until  the  seventh  month,  when  a  retrogressive  metamorphosis  takes  place 
until  its  separation  during  labor,  at  which  time  it  is  of  an  oval  or  rounded 
shape,  and  measures  from  seven  to  nine  inches  in  length,  six  to  eight 
inches  in  breadth,  and  weighs  from  fifteen  to  twenty  ounces.  It  is  most 
frequently  situated  at  the  upper  and  posterior  part  of  the  inner  surface  of 
the  uterus. 

The  placenta  consists  of  two  portions,  a  foetal  and  a  maternal. 

The  Fatal  portion  is  formed  by  the  villi  of  the  chorion,  which,  by  devel- 
oping, rapidly  increase  in  size  and  number.  They  become  branched  and 
penetrate  the  uterine  tubules,  which  enlarge  and  receive  their  many  ramifi- 
cations. The  capillary  blood  vessels  in  the  anterior  of  the  villi  also  enlarge 
and  freely  anastomose  with  each  other. 

The  Maternal  portion  is  formed  from  that  part  of  the  hypertrophied  and 
vascular  decidual  membrane  between  the  ovum  and  the  uterus,  the  decidua 
serotina.  As  the  placenta  increases  in  size,  the  maternal  blood  vessels 
around  the  tubules  become  more  and  more  numerous,  and  gradually  fuse 
together,  forming  great  lakes,  which  constitute  sinuses  in  the  walls  of  the 
uterus. 

As  the  latter  period  of  gestation  approaches,  the  villi  extend  deeper  into 
the  decidua,  while  the  sinuses  in  the  maternal  portion  become  larger  and 
extend  further  into  the  chorion.  Finally,  from  excessive  development  ot 
the  blood  vessels,  the  structures  between  them  disappear,  and  as  their  walls 
come  in  contact,  they  fuse  together,  so  that,  ultimately,  the  maternal  and 
foetal  blood  are  only  separated  by  a  thin  layer  of  a  homogeneous  substance. 
When  fully  formed,  the  placenta  consists  principally  of  blood  vessels  inter- 
lacing in  every  direction.  The  blood  of  the  mother  passes  from  the  uterine 
vessels  into  the  lakes  surrounding  the  villi;  the  blood  from  the  child  flows 
from  the  umbilical  arteries  into  the  interior  of  the  villi;  but  there  is  not  at 
any  time  an  intermingling  of  blood,  the  two  being  separated  by  a  delicate 
membrane  formed  by  a  fusion  of  the  walls  of  the  blood  vessels  and  the 
walls  of  the  villi  and  uterine  sinuses. 

The  function  of  the  placenta,  besides  nutrition,  is  that  of  a  respiratory 
organ,  permitting  the  oxygen  of  the  maternal  blood  to  pass  by  osmosis 
through  the  delicate  placental  membrane  into  the  blood  of  the  foetus ;  at 
the  same  time  permitting  the  carbonic  acid  and  other  waste  products,  the 


DEVELOPMENT   OF   THE   EMBRYO.  185 

result  of  nutritive  changes  in  the  foetus,  to  pass  into  the  maternal  blood,  and 
so  to  be  carried  to  the  various  eliminating  organs. 

Through  the  placenta  also  passes  all  the  nutritious  materials  of  the 
maternal  blood  which  are  essential  for  the  development  of  the  embryo. 

At  about  the  middle  of  gestation  there  develops  beneath  the  decidual 
membrane  a  new  mucous  membrane,  destined  to  perform  the  functions  of 
the  old  when  it  is  extruded  from  the  womb,  along  with  the  other  embryonic 
structures,  during  parturition. 


DEVELOPMENT  OF  THE  EMBRYO. 

Nervous  System.  The  cerebro -spinal  axis  is  formed  within  the  me- 
dullary canal  by  the  development  of  cells  from  its  inner  surfaces,  which 
as  they  increase  fall  up  the  canal,  and  there  remains  only  the  central  canal 
of  the  cord.  The  external  surface  gives  rise  to  the  dura  mater  and  pia 
mater.  The  neural  canal  thus  formed  is  a  tubular  membrane;  it  terminates 
posteriorly  in  an  oval  dilatation,  and  anteriorly  in  a  bulbous  extremity, 
which  soon  becomes  partially  contracted,  and  forms  the  anterior,  middle 
and  posterior  cerebral  vesicles,  from  which  are  ultimately  developed  the 
cerebrum,  the  corpora  quadrigemina,  and  medulla  oblongata,  respectively. 

The  anterior  vesicle  soon  subdivides  into  two  secondary  vesicles,  the 
larger  of  which  becomes  the  hemispheres,  the  smaller,  the  optic  thalami ; 
the  posterior  vesicle  also  divides  into  two;  the  anterior  becoming  the  cere- 
bellum, the  posterior,  the  pons  Varolii  and  medulla  oblongata. 

About  the  seventh  week  the  straight  chain  of  cerebral  vesicles  becomes 
curved  from  behind  forward  and  forms  three  prominent  angles.  As  devel- 
opment advances,  the  relative  size  of  the  encephalic  masses  changes.  The 
cerebrum  developing  more  rapidly  than  the  posterior  portion  of  the  brain, 
soon  grows  backward  and  arches  over  the  optic  thalami  and  the  tubercula 
quadrigemina;  the  cerebellum  overlaps  the  medulla  oblongata. 

The  surface  of  the  cerebral  hemispheres  is  at  first  smooth,  but  at  about 
the  fourth  month  begins  to  be  marked  by  the  future  fissures  and  convolutions. 

The  Eye  is  formed  by  a  little  bud  projecting  from  the  side  of  the 
anterior  vesicle.  It  is  at  first  hollow,  but  becomes  lined  with  nervous 
matter,  forming  the  optic  nerve  and  retina  ;  the  remainder  of  the  cavity  is 
occupied  by  the  vitreous  body.  The  anterior  portion  of  the  pouch  becomes 
invaginated  and  receives  the  crystalline  /ens,  which  is  a  product  of  the 
epiblast,  as  is  also  the  cornea.  The  iris  appears  as  a  circular  membrane 
without  a  central  aperture,  about  the  seventh  week;  the  eyelids  are  formed 
between  the  second  and  third  months. 
M 


186  HUMAN    PHYSIOLOGY. 

The  Internal  Ear  is  developed  from  the  auditory  vesicle,  budding  from 
the  third  cerebral  vesicle;  the  membranous  vestibule  appears  first,  and  from 
it  diverticula  are  given  off,  which  become  the  semicircular  canals  and 
cochlea. 

The  cavity  of  the  tympanum,  the  Eustachian  tube,  and  the  external 
auditory  canal  are  the  remains  of  the  first  branchial  cleft;  the  cavity  of  this 
cleft  being  subdivided  into  the  tympanum  and  external  auditory  meatus  by 
the  membrana  tympani. 

The  Skeleton.  The  chorda  dorsalis,  the  primitive  part  of  the  vertebral 
column,  is  a  cartilaginous  rod  situated  beneath  the  medullary  groove.  It  is 
a  temporary  structure,  and  disappears  as  the  true  bony  vertebrae  develop. 
On  either  side  are  the  quadrate  masses  of  the  mesoblast,  the  primitive  ver- 
tebrae, which  send  processes  upward  and  around  the  medullary  groove,  and 
downward  and  around  the  chorda  dorsalis,  forming  in  these  situations  the 
arches  arid  bodies  of  the  future  vertebrae. 

More  externally  the  outer  layer  of  the  mesoblast  and  epiblast  arch  down- 
ward and  forward,  forming  the  ventral  laminae,  in  which  develop  the 
muscles  and  bones  of  the  abdominal  walls. 

The  true  cranium'vs,  an  anterior  development  of  the  vertebral  column,  and 
consists  of  the  occipital,  parietal  and  frontal  segments,  which  correspond  to 
the  three  cerebral  vesicles.  The  base  of  the  cranium  consists,  at  this  period, 
of  a  cartilaginous  rod  on  either  side  of  the  anterior  extremity  of  the  chorda 
dorsalis,  in  which  three  centres  of  ossification  appear,  the  basi-  occipital,  the 
basi-sphenoidal,  and  the  pre-sphenoidal.  They  ultimately  develop  into  the 
basilar  process  of  the  occipital  bone  and  the  body  of  the  sphenoid. 

The  entire  skeleton'^  at  first  either  membranous  or  cartilaginous.  At  the 
beginning  of  the  second  month  centres  of  ossification  appear  in  the  jaws  and 
clavicle;  as  development  advances,  the  ossific  points  in  all  the  future  bones 
extend,  until  ossification  is  completed. 

The  limbs  develop  from  four  little  buds  projecting  from  the  sides  of  the 
embryo,  which,  as  they  increase  in  length,  separate  into  the  thigh,  leg  and 
foot,  and  the  arm,  forearm  and  hand ;  the  extremities  of  the  limbs  undergo 
subdivision,  to  form  the  fingers  and  toes. 

Face  and  Visceral  Arches.  In  the  facial  and  cervical  regions  the 
visceral  laminae  send  up  three  processes,  the  visceral  arches,  separated  by 
clefts,  the  visceral  clefts. 

T&z  first,  or  the  mandibular  arches,  unite  in  the  median  line  to  form  the 
lower  jaw,  and  superiorly  form  the  malleus.  A  process  jutting  from  its 
base  grows  forward,  unites  with  the  fronto-nasal  process  growing  from 


DEVELOPMENT   OF   THE    EMBRYO.  187 

above,  and  forms  the  upper  jaw.  When  the  superior  maxillary  processes 
fail  to  unite,  there  results  the  cleft-palate  deformity ;  if  the  integument  also 
fails  to  unite,  there  results  the  hare-lip  deformity.  The  space  above  the 
mandibular  arch  becomes  the  mouth. 

The  second  arch  develops  the  incus  and  stapes  bones,  the  styloid  process 
and  ligament,  and  the  lesser  cornu  of  the  hyoid  bone.  The  cleft  between 
the  first  and  second  arches  partially  closes  up,  but  there  remains  an  opening 
at  the  side  which  becomes  the  Eustachian  tube,  tympanic  cavity,  and  exter- 
nal auditory  meatus. 

The  third  arch  develops  the  body  and  greater  cornu  of  the  hyoid 
bone. 

Alimentary  Canal  and  its  Appendages.  The  alimentary  canal  is 
formed  by  a  pinching  off  of  the  yelk  sac  by  the  visceral  plates  as  they  grow 
downward  and  forward.  It  consists  of  three  distinct  portions,  the  fore  gut, 
the  hind  gut,  and  the  central  part,  which  communicates  for  some  time  with 
the  yelk  sac.  It  is  at  first  a  straight  tube,  closed  at  both  extremities,  lying 
just  beneath  the  vertebral  column.  The  canal  gradually  increases  in 
length,  and  becomes  more  or  less  convoluted;  at  its  anterior  portion  two 
pouches  appear,  which  become  the  cardiac  and  pyloric  extremities  of  the 
stomach.  At  about  the  seventh  week  the  inferior  extremity  of  the  intestine 
is  brought  into  communication  with  the  exterior,  by  an  opening,  the  anus. 
Anteriorly  the  mouth  and  pharynx  are  formed  by  an  involution  of  epiblast, 
which  deepens  until  it  communicates  with  the  fore  gut. 

The  Liver  appears  as  a  slight  protrusion  from  the  sides  of  the  alimentary 
canal,  about  the  end  of  the  first  month ;  it  grows  very  rapidly,  attains  a 
large  size,  and  almost  fills  up  the  abdominal  cavity.  The  hepatic  cells  are 
derived  from  the  intestinal  epithelium,  the  vessels  and  connective  tissue 
from  the  mesoblast. 

The  Pancreas  is  formed  by  the  hypoblastic  membrane.  It  originates  in 
two  small  ducts  budding  from  the  duodenum,  which  divide  and  subdivide, 
and  develop  the  glandular  structure. 

The  Lungs  are  developed  from  the  anterior  part  of  the  oesophagus.  At 
first  a  small  bud  appears,  which,  as  it  lengthens,  divides  into  two  branches ; 
secondary  and  tertiary  processes  are  given  off  these,  which  form  the  bron- 
chial tubes  and  air  cells.  The  lungs  originally  extended  into  the  abdomi- 
nal cavity,  but  become  confined  to  the  thorax  by  the  development  of  the 
diaphragm. 

The  Bladder  is  formed  by  a  dilatation  of  that  portion  of  the  allantois 
remaining  within  the  abdominal  cavity.  It  is  at  first  pear-shaped,  and 
communicates  with  the  intestine,  but  later  becomes  separated,  and  opens 


188  HUMAN  PHYSIOLOGY. 

exteriorly   by  the  urethra.     It   is  attached   to   the  abdominal  walls  by  a 
rounded  cord,  the  urachus,  the  remains  of  a  portion  of  the  allantois. 

Genito-urinary  Apparatus.  The  Wolffian  bodies  appear  about  the 
thirteenth  day,  as  long  hollow  tubes  running  along  each  side  of  the  primi- 
tive vertebral  column.  They  are  temporary  structures,  and  are  sometimes 
called  the  primordial  kidneys.  The  Wolffian  bodies  consist  of  tubules 
which  run  transversely  and  are  lined  with  epithelium;  internally  they 
become  invaginated  to  receive  tufts  of  blood  vessels ;  externally  they  open 
into  a  common  excretory  duct,  the  duct  of  the  Wolffian  body,  which  unites 
with  the  duct  of  the  opposite  body,  and  empties  into  the  intestinal  canal 
at  a  point  opposite  the  allantois.  On  the  outer  side  of  the  Wolffian  body 
there  appears  another  duct,  the  duct  of  Miiller,  which  also  opens  into  the 
intestine. 

Behind  the  Wolffian  bodies  are  developed  the  structures  which  become 
either  the  ovaries  or  testicles.  In  the  development  of  the  female,  the 
Wolffian  bodies  and  their  ducts  disappear;  the  extremities  of  the  M.iillerian 
ducts  dilate  and  form  the  fimbriated  extremity  of  the  Fallopian  tubes,  while 
the  lower  portions  coalesce  to  form  the  body  of  the  uterus  and  vagina, 
which  now  separate  themselves  from  the  intestine. 

In  the  development  of  the  male,  the  Miillerian  ducts  atrophy,  and  the 
ducts  of  the  Wolffian  body  ultimately  form  the  epididymis  and  vas  deferens. 
About  the  seventh  month  the  testicles  begin  to  descend,  and  by  the  ninth 
month  have  passed  through  the  abdominal  ring  into  the  scrotum. 

The  Kidneys  are  developed  out  of  the  Wolffian  bodies.  They  consist  of 
little  pyramidal  lobules,  composed  of  tubules  which  open  at  the  apex  into 
the  pelvis.  As  they  pass  outward  they  become  convoluted  and  cup-shaped 
at  their  extremities,  receive  a  tuft  of  blood  vessels,  and  form  the  Mal- 
pighian  bodies. 

The  ureters  are  developed  from  the  kidneys,  and  pass  downward  to  be 
connected  with  the  bladder. 

The  Circulatory  Apparatus  assumes  three  different  forms  at  different 
periods  of  life,  all  having  reference  to  the  manner  in  which  the  embryo 
receives  nutritious  matter  and  is  freed  of  waste  products. 

The  Vitelline  circulation  appears  first  and  absorbs  nutritious  material 
from  the  vitellus.  It  is  formed  by  blood  vessels  which  emerge  from  the 
body  and  ramify  over  a  portion  of  the  vitelline  membrane,  constituting  the 
area  vasctdosa.  The  heart,  lying  in  the  median  line,  gives  off  two  arches 
which  unite  to  form  the  abdominal  aorta,  from  which  two  large  arteries 
are  given  off,  passing  into  the  vascular  area ;  the  venous  blood  is  returned 


INDEX. 


ABDUCENS  NERVE 
**•     Aberration,  chromatic 

spherical 

Absorption 

by  the  lacteals 

by  the  blood  vessels 42 

of  oxygen  in  respiration  ... 

Accommodation  of  the  eye 

Adipose  tissue,  uses  of  in  the  body    . 
Adult  circulation,  establishment  of  at 

birth 

Air,  atmospheric,  composition  of  .    . 
amount  exchanged  in  respira- 
tion   

changes  in  during  respiration 

Albumin,  uses  of  in  the  body   ....      14 

Albuminoid  substances 14 

Alcohol,  action  of 22 

Alimentary  principles,  classification  of    21 

albuminous  principles    ....      21 

saccharine  principles 22 

oleaginous  principles 22 

nlei 


VGE 

X25 

163 
163 

37 
42 
42 
65 
162 
13 

190 
65 

64 
66 

P 
/CANALS  OF  CUVIER    .... 
^    Capillary  blood  vessels  

\<;ii 
189 

57 
133 

'33 
17 
18 
118 

iS 

137 
140 

J43 
143 
144 

Caudate  nucleus  
Cells,  structure  of  
manifestations  of  life  by   .    .    . 
of  anterior  horns  of  gray  matter 
Centre  for  articulate  language  .... 

—  —  motor  area  of  

•  inorganic  principles 


Alimentary  canal,  development  of  .    . 

Allantois,  development  and  function  of  182 

Amnion,  formation  of 

Animal  heat  .    .    .    .    • 

Anterior  columns  of  spinal  cord 

Area,  germinal 

Arteries,  properties  of 

Asphyxia 

Astigmatism 

Axis,  cerebro-spinal 
cylinder  of  nerves 


"RILE 

-1-*     Bladder,  urinary 

Blastodermic  membranes 

Blood  

composition  of  plasma  .... 

coagulation  of 

coloring  matter  of 

— — —  changes  in,  during  respiration 

circulation  of 

rapidity  of  flow  in  arteries  .  . 

rapidity  of  flow  in  capillaries  . 

pathological  conditions  of  .  . 

.  corpuscles 

origin  of 

pressure 

Burdach,  column  of 


Cerebellum 134 

forced  movements  of 135 

Cerebral  vesicles  of  embryo 185 

Chemical  composition  of  human  body  10 

elements,  proximate  quantity 

of  in  body 17 

Chorda  dorsalis 181 

tympani  nerve,  course  and  func- 


182        Chorion  

183 

182        Chyle  

67 

Ciliary  muscle  

162 

117 

Circulation  of  blood  

gj 

181 

Claustrum  

*33 

56 

Cochlea  

171 

66 

Columns  of  spinal  cord  

117 

163 

Corium  

88 

"5 

Corpora  Wolffiana  

188 

93 

quadrigemina  
Corpus  luteum  . 

132 
177 

striatum  

133 

36 

7Q 

Corti,  organ  of  
Cranial  nerves 

172 
1  02 

18? 

Crura  cerebri  

45 

Crystalline  lens 

X59 

& 

T}ECIDUAL  MEMBRANE  .   . 
••^     Decussation  of  motor  and  sen- 

183 

5T 

sory  fibres                  •«.*••. 

119 

'*• 
C7 

Deglutition 

V 

28 

58 

nervous  circle  of  

129 

50 

I 

Development  of  accessory  structures 
of  embryo  
Digestion    

1  80 
24 

Ductus  arteriosus  ..."  

189 

118 

venosus  

189 

195 


196 


INDEX. 


r 

PAR  

•*-*  Electrotonus  
Embryo,  development  of  
Endolymph  
Epidermis  
Epididymis  

AGE 

165 

100 

185 

172 

88 
179 
29 
168 
76 
154 
160 
164 

108 

ICQ 
I76 

37 
«4 

176 

137 
19 
23 
23 

21 
22 
22 
22. 
l64 

IOI 

p 
Heart,  ganglia  of  

AGE 

55 
54 
54 
52 

55 
154 
163 
114 

167 
26 
28 
62 
133 
i33 
34 

'I6 
163 

139 

76 
80 

orce  exerted  by  left  ventricle 

°               fMnJLl'rti     '     *  Vi' 

course  ot  Dloou  tnroufen    .    .    . 

upon  

Epiglottis  
Eustachian  tube  .  

Hypermetropia  
Hypoglossal  nerve 

Excretion   . 
Eye  .... 

TNCUS  BONE 

T^ACIAL  NERVE 

•*•  Insalivation  

Inspiration,  movements  of  thorax  in  . 
Internal  capsule  

—  —  —  paralysis,  symptoms  of  . 
Fallopian  tubes  
Faeces  

Fat,  uses  of  in  the  body  
Female  organs  of  generation  .... 
Fissures  and  convolutions  of  brain  .  . 
Food  

Iris  

action  of  
Island  of  Reil  

T^IDNEYS 

percentage  composition  of  .  . 

•"•^  excretion  of  urine  by  .  . 

LABYRINTH  OF  INTERNAL 
ear  

aiDuimnous  principle.,  oi  .   .   . 

.,acc   am                     s  ot    .    .    . 

inorganic  principles  of  ... 

("*  ALVANIC  CURRENTS,  EF- 
^-*     feet  on  nerves  

function  of  cochlea  
function  of  semicircular  canals 
Language,  articulate,  centre  for  .  .  . 

171 
170 
M5 
173 
117 

IOI 

'59 

12 
83 
85 

86 
87 
84 

J43 
60 

66 
43 
39 
39 

72 
1  66 
25 
25 
25 
127 
126 
172 
1  66 
177 
1  66 
73 
M3 

f 
163 

Ganglia  

I48 
I48 
I48 
I48 
I48 
I48 
149 

11 
31 
32 
179 
176 
47 
43 
77 
no 

86 

% 

93 

89 
47 
165 
51 
5i 
53 

55 

Lateral  columns  of  spinal  cord  .  .  . 
Laws  of  muscular  contraction  .  .  . 
Lens,  crystalline  
Lime  phosphate  

Gasserian  

otic  

semi-lunar  

glycogenic  function  of  .... 

Gastric  juice  

Localization  of  functions  in  cerebrum 

Generation,  male  organs  of  

changes  in  blood  while  passing 

Globules  of  the  blood  

Lymphatic  glands  .  
vessels,  origin  and  course  of  . 

TV/TAMMARY  GLANDS  .... 
1VJ-  Malleus  bone  
Mastication 

Glomeruli  of  the  kidneys  
Glosso-pharyngeal  nerve  
Glottis,  respiratory  movements  of  ,  . 
Glycogen  
Glycogenic  function  of  liver  
Goll,  column  of  
Graafian  follicles 

Gray  matter  of  nervous  system  .  .  . 
TTAIR  .... 

ncrj  .        IT       °    

Membrana  basilaris  
tympani  
Menstruation  
Middle  ear  

Milk 

Haemoglobin  
Hearing,  sense  of  
Heart 

Motor  centres  of  cerebrum  
Muscles,  properties  of  
Myopia  

nerve  upon  

INDEX. 


197 


TVJERVE,  OLFACTORY  .    .    . 

•*•'      optic    .    .    . 

motor  oculi 

pathetic 

trigeminal 

abducens    

facial 

auditory 

glosso-pharyngeal,     .... 

pneumogastric 

spinal  accessory  ..    .    .    .    . 

hypoglossal 

cells,  structure  of 

fibres,  terminations  of  ... 

force,  rate  of  transmission  of 

roots,  function  of  anterior  and 

posterior 

Nerves,  centrifugal  and  centripetal, 

cranial 

decussation  of  motor  and  sen- 
sory   

vaso-motor 

properties  and  functions  of . 

spinal . 


PAGE 
.  102 
.  103 
.  104 

•  I05 
.    106 
.    105 

108 

.  109 

.  no 

.  Ill 

•  "3 

•  "4 
.  92 

•  94 
.      98 

.  118 
95,96 


Nervous  system 

white  and  gray  matter  of .   . 

cerebro-spinal 

sympathetic 

Nucleus  caudatus 

lenticularis 


119 
129 

95 
118 

92 

93 
92 

147 
133 
133 


QLFACTORY  NERVES  . 
^*-'     Ophthalmic  ganglion    .    . 

Optic  nerves 

thalamus 

functions  of  . 


102 
148 
103 
133 
J34 

Organs  of  Corti 172 

Otic  ganglion 148 

Ovaries 176 

Ovum 176 

discharge  of  from  the  ovary    .    177 

Oxygen,  absorption  of  by  haemoglobin     47 


pACINIAN  CORPUSCLES  .    .  95 

^     Pancreatic  juice 35 

Patheticus  nerve 105 

Peptones 32 

Perilymph 171 

Perspiration 90 

Petrosal  nerves,  large  and  small .    .    .  108 

Phonation 174 

Physiology,  definition  of 9 

Placenta,  formation  and  function  of  .  181 

Pneumogastric  nerve 1 1 1 

Pons  varolii 131 

Portal  vein 37 

Posterior  columns  of  spinal  cord    .    .  117 

— — —  functions  of 122 

Prehension 25 

Presbyopia 163 

Pressure  of  blood  in  arteries 56 


Proximate  principles 

inorganic 

organic,  non-nitrogenized    . 

organic,  nitrogenized     .    .    . 

of  waste 

quantity  of  chemical  elements 

in  body 

Ptyalin 

Pulse 

Pyramidal  tracts 


•RED  CORPUSCLES  OF 

**>    blood 

Reflex  movements  of  spinal  cord    . 

action,  laws  of 

Reproduction 

Respiration 

movements  of 

nervous  mechanism  of  ... 

types  of 

nervous  circle  of  ...... 

Retina  .   . 


PAGE 
ii 


17 
27 
57 
119 


47 
123 
124 
176 

59 
62 
63 
63 
130 


eALIVA 

^     Sebaceous  glands 

Secretion 

Semi-circular  canals 

Semen 

Sight,  sense  of 

Skin .. 

relative  sensibility  of     .... 

Smell,  sense  of 

Sounds  of  heart 

Spermatozoa 

Spheno-palatine  ganglion 

Spinal  accessory  nerve 

Spinal  cord 

membranes  of 

structure  of  white  matter  .    .    . 

— — —  structure  of  gray  matter  .    .    . 

properties  of 

function  of  as  a  conductor  .    . 

as  an  independent  centre     .    . 

decussation  of  motor  and  sen- 


sory  fibres 

reflex  action  of 


•  special  centres  of 

paralysis,  from  injuries  of    .    . 

nerves,  origin  of 

course  of  anterior  and  posterior 

roots  of 

Spleen 

Starvation,  phenomena  of 

Stomach • 

Structural  composition  of  the  body  . 

Submaxillary  ganglion 

Sugar,  uses  of  in  the  body 

Supra-renal  capsules 

Sudoriparous  glands 

Sympathetic  nervous  system  .... 
properties  and  functions  of  .    . 


27 

|9 
69 
171 
180 
154 


116 
117 
118 

121 
122 
122 

II9 
I23 
125 
126 
I19 

II9 

74 

20 
29 

H8? 

13 

75 
90 
147- 
149 


198 


INDEX. 


I 
'JVA.STE,  SENSE  OF  

AGE 

152 
153 
25 
170 
179 
41 
62 
18 
152 
153 
'53 
151 
119 

183 
81 
82 
80 
80 

81 

Urination,  nervous  mechanism  of  . 
Uterus     

VAPOR,  WATERY,  OF 
v      breath         .   . 

PAGE 

•      79 
•    "7 

66 

Teeth  
Tensor  tympani  muscle  

Testicles  
Thoracic  duct   
Thorax,  enlargement  of  in  inspiration 
Tissues,  classification  of   

Vascular  glands    

74 
188 
.    129 
•      58 
.    179 
132 
146 
64 
174 
173 

12 

1  88 

Tongue    .    .               

Vaso-motor  nerves,  origin  of   . 
Veins   

Touch,  sense  of    
Tiirck,  column  of    

UMBILICAL  CORD     . 
Urea  
Uric  acid    
Urine 

Vesiculae  seminales  
Vision,  physical  centre  for    .... 

Vital  capacity  of  lungs  
Vocal  cords    .    . 

Voice 

WATER,  AMOUNT  OF  IN 
body     

Wolffian  bodies     

ents  secreted  daily   

REDUCED  FAC-SIMILE I  A        N     F\V 

OF  TITLE  PAGE.       j 


MEDICAL  DICTIONARY 


INCLUDING  ALL  THE  WORDS  AND  PHRASES  GENERALLY 
USED  IN  MEDICINE,  WITH  THEIR  PROPER  PRO- 
NUNCIATION AND  DEFINITIONS. 


BASED  ON  RECENT  MEDICAL,  LITERATURE. 


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OPHTHALMIC  SURGEON  TO  THE  PHILADELPHIA  HOSPITAL  AND  CLINICAL  CHIEF 
OFHTHALMOLOCICAL  DEPARTMENT,  GERMAN  HOSPITAL, 


WITH    ELABORATE   TABLES  OP  THB  BACILLI,  MICROCOCCI,  LEUCOMA'l'NES,  PTOMAINES, 

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A  CATALOGUE 

OF 

BOOKS  FOR  STUDENTS. 


INCLUDING  THE 


PQULZ-COMPENDS? 


CONTENTS. 

PAGE 

PAGE 

New  Series  of  Manuals,  2,3 

4,5 

Obstetrics.     . 

10 

Anatomy, 

6 
ii 

6 
7 

Pathology,  Histology, 
Pharmacy,     . 
Physiology,  . 
Practice  of  Medicine, 

ii 

ii 

12 
II 
12 

Chemistry,     . 
Children's  Diseases, 

Dentistry,      . 

8 

Prescription  Books, 

12 

Dictionaries, 
Eye  Diseases, 

8 
9 

PQuiz-Compends? 
Skin  Diseases,       .  . 

14 

15 

12 

Electricity,    . 

9 

Surgery, 

J3 

Gynaecology, 

10 

Therapeutics, 

Q 

9 
9 

Urine  and  Urinary  Organs,     13 
Venereal  Diseases,        .        .  13 

Materia  Medica,  . 

Medical  Jurisprudence 

10 

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"  An  excellent  Series  of  Manuals." — Archives  of  Gynaecology. 

A  NEW  SERIES  OF 

STUDENTS'    MANUALS 

On  the  various  Branches  of  Medicine  and  Surgery. 

Can  be  used  by  Students  of  any  College. 
Price  of  each,  Handsome  Cloth,  $3.00.    Full   Leather,  $3.50. 

The  object  of  this  series  is  to  furnish  good  manuals 
for  the  medical  student,  that  will  strike  the  medium 
between  the  compend  on  one  hand  and  the  prolix  text- 
book on  the  other — to  contain  all  that  is  necessary  for 
the  student,  without  embarrassing  him  with  a  flood  of 
theory  and  involved  statements.  They  have  been  pre- 
pared by  well-known  men,  who  have  had  large  experience 
as  teachers  and  writers,  and  who  are,  therefore,  well 
informed  as  to  the  needs  of  the  student. 

Their  mechanical  execution  is  of  the  best — good  type 
and  paper,  handsomely  illustrated  whenever  illustrations 
are  of  use,  and  strongly  bound  in  uniform  style. 

Each  book  is  sold  separately  at  a  remarkably  low 
price,  and  the  immediate  success  of  several  of  the 
volumes  shows  that  the  series  has  met  with  popular 
favor. 

No.  1.     SURGERY.     236  Illustrations. 
A   Manual   of   the   Practice  of    Surgery.     By  WM.  J. 

WALSHAM,  M.D.,  Asst.  Surg.  to,  and  Demonstrator  of 

Surg.   in,  St.   Bartholomew's  Hospital,  London,  etc. 

228  Illustrations. 

Presents  the  introductory  facts  in  Surgery  in  clear,  precise 
language,  and  contains  all  the  latest  advances  in  Pathology, 
Antiseptics,  etc. 

"  It  aims  to  occupy  a  position  midway  between  the  pretentious 
manual  and  the  cumbersome  System  of  Surgery,  and  its  general 
character  may  be  summed  up  in  one  word — practical." — The  Medi- 
cal Bulletin, 

"  Walsham,  besides  being  an  excellent  surgeon,  is  a  teacher  in 
its  best  sense,  and  having  had  very  great  experience  in  the 
preparation  of  candidates  for  examination,  and  their  subsequent 
professional  career,  may  be  relied  upon  to  have  carried  out  his 
work  successfully.  Without  following  out  in  detail  his  arrange- 
ment, which  is  excellent,  we  can  at  once  say  that  his  book  is  an 
embodiment  of  modern  ideas  neatly  strung  together,  with  an  amount 
of  careful  organization  well  suited  to  the  candidate,  and,  indeed,  to 
the  practitioner." — British  Medical  Journal. 

Price  of  each  Book,  Cloth,  $3.00 ;  Leather,  $3.50. 


THE  NEW  SERIES  OF  MANUALS. 


No.  2.    DISEASES  OF  -WOMEN.    ISO  Illus. 

NEW     EDITION. 

The  Diseases  of  Women.  Including  Diseases  of  the 
Bladder  and  Urethra.  By  DR.  F.  WINCKEL,  Professor 
of  Gynaecology  and  Director  of  the  Royal  University 
Clinic  for  Women,  in  Munich.  Second  Edition.  Re- 
vised and  Edited  by  Theophilus  Parvin,  M.D., 
Professor  of  Obstetrics  and  Diseases  of  Women  and 
Children  in  Jefferson  Medical  College.  150  Engrav- 
ings, most  of  which  are  original. 
"  The  book  will  be  a  valuable  one  to  physicians,  and  a  safe  and 

satisfactory  one  to  put  into  the  hands  of  students.     It  is  issued  in  a 

neat  and  attractive  form,  and  at  a  very  reasonable  price." — Boston 

Medical  and  Surgical  Journal. 

No.  3.    OBSTETRICS.    227  Illustrations. 

A  Manual  of  Midwifery.     By  ALFRED  LEWIS  GALABIN, 
M.A.,  M.D.,  Obstetric  Physician  and  Lecturer  on  Mid- 
wifery and  the  Diseases  of  Women  at  Guy's  Hospital, 
London;     Examiner   in    Midwifery   to   the   Conjoint 
Examining  Board  of  England,  etc.     With  227  Illus. 
"  This  manual  is  one  we  can  strongly  recommend  to   all    who 
desire  to  study  the  science  as  well  as  the  practice  of  midwifery. 
Students   at  the  present  time  not  only  are  expected  to  know  the 
principles  of  diagnosis,  and  the  treatment  of  the  various  emergen- 
cies and  complications  that  occur  in  the  practice  of  midwifery,  but 
find  that   the   tendency  is   for  examiners  to  ask  more  questions 
relating  to  the  science  of  the  subject  than  was  the  custom  a  few 
years   ago.  *  *  *    The  general  standard  of  the  manual  is  high; 
and  wherever  the  science  and  practice  of  midwifery  are  well  taught 
it  will  be  regarded  as  one  of  the  most  important  text-books  on  the 
subject." — London  Practitioner. 

No.  4.    PHYSIOLOGY.    Fifth  Edition. 

321  ILLUSTRATIONS  AND  A  GLOSSARY. 
A  Manual  of  Physiology.  By  GERALD  F.  YEO,  M.D., 
F.R.C  S.,  Professor  of  Physiology  in  King's  College, 
London.  321  Illustrations  and  a  Glossary  of  Terms. 
Fifth  American  from  last  English  Edition,  revised  and 
improved.  758  pages. 

This  volume  was  specially  prepared  to  furnish  students  with  a 
new  text-book  of  Physiology,  elementary  so  far  as  to  avoid  theories 
which  have  not  borne  the  test  of  time  and  such  details  of  methods 
AS  are  unnecessary  for  students  in  our  medical  colleges. 

"The  brief  examination  I  have  given  it  was  so  favorable  that  I 
placed  it  in  the  list  of  text-books  recommended  in  the  circular  of  the 
University  Medical  College."— Prof.  Lewis  A.  Stimson,  M.D.. 
37  East  33d  Street,  New  York. 

Price  of  each  Book,  Cloth,  $3.00;  Leather,  $3.50. 


THE  NEW  SERIES  OF  MANUALS. 


No.  5.    DISEASES  OF  CHILDREN. 

SECOND  EDITION. 

A  Manual.  By  J.  F.  GOODHART,  M.D.,  Phys.  to  the 
Evelina  Hospital  for  Children;  Asst.  Phys.  to 
Guy's  Hospital,  London.  Second  American  Edition. 
Edited  and  Rearranged  by  Louis  STARR,  M.D.,  Clinical 
Prof,  of  Dis.  of  Children  in  the  Hospital  of  the  Univ. 
of  Pennsylvania,  and  Physician  to  the  Children's  Hos- 
pital, Phila.  Containing  many  new  Prescriptions,  a  list 
of  over  50  Formulae,  conforming  to  the  U.  S.  Pharma- 
copoeia, and  Directions  for  making  Artificial  Human 
Milk,  for  the  Artificial  Digestion  of  Milk,  etc.  Illus. 

"  The  merits  of  the  book  are  many.  Aside  from  the  praiseworthy 
•work  of  the  printer  and  binder,  which  gives  us  a  print  and  page 
that  delights  the  eye,  there  is  the  added  charm  of  a  style  of  writ- 
ing that  is  not  wearisome,  that  makes  its  statements  clearly  and 
forcibly,  and  that  knows  when  to  stop  when  it  has  said  enough. 
The  insertion  of  typical  temperature  charts  certainly  enhances  the 
value  of  the  book.  It  is  rare,  too,  to  find  in  any  text-book  so  many 
topics  treated  of.  All  the  rarer  and  out-of-the-way  diseases  are 
given  consideration.  This  we  commend.  It  makes  the  work 
valuable." — Archives  of  Pedriatics ,  July ,  i8qo. 

"  The  author  has  avoided  the  not  uncommon  error  of  writing  a. 
book  on  general  medicine  and  labeling  it  '  Diseases  of  Children,' 
but  has  steadily  kept  in  view  the  diseases  which  seemed  to  be 
incidental  to  childhood,  or  such  points  in  disease  as  appear  to  be  so 
peculiar  to  or  pronounced  in  children  as  to  justify  insistence  upon 
them.  *  *  *  A  safe  and  reliable  guide,  and  in  many  ways 
admirably  adapted  to  the  wants  of  the  student  and  practitioner." — 
American  Journal  of  Medical  Science. 

"  Thoroughly  individual,  original  and  earnest,  the  work  evi- 
dently of  a  close  observer  and  an  independent  thinker,  this  book, 
though  small,  as  a  handbook  or  compendium  is  by  no  means  made 
up  of  bare  outlines  or  standard  facts." — The  Therapeutic  Ga- 
zette. 

"As  it  is  said  of  some  men,  so  it  might  be  said  of  some  books, 
that  they  are  '  born  to  greatness.'  This  new  volume  has,  we 
believe,  a  mission,  particularly  in  the  hands  of  the  younger 
members  of  the  profession.  In  these  days  of  prolixity  in  medical 
literature,  it  is  refreshing  to  meet  with  an  author  who  knows  both 
what  to  say  and  when  he  has  said  it.  The  work  of  Dr.  Goodhart 
(admirably  conformed,  by  Dr.  Starr,  to  meet  American  require- 
ments) is  the  nearest  approach  to  clinical  teaching  without  the 
actual  presence  of  clinical  material  that  we  have  yet  seen." — New 
York  Medical  Record. 

Price  of  each  Book,  Cloth,  $3.00  :  Leather,  $3.50. 


THE  NEW  SERIES  OF  MANUALS. 


No.  6.    PRACTICAL  THERAPEUTICS. 

FOURTH  EDITION,  WITH  AN  INDEX  OF  DISEASES. 

Practical  Therapeutics,  considered  with  reference  to 
Articles  of  the  Materia  Medica.  Containing,  also,  an 
Index  of  Diseases,  with  a  list  of  the  Medicines 
applicable  as  Remedies.  By  EDWARD  JOHN  WARING, 
M.D.,  F.R.C.P.  Fourth  Edition.  Rewritten  and  Re- 
vised by  DUDLEY  W.  BUXTON,  M.D.,  Asst.  to  the  Prof, 
of  Medicine  at  University  College  Hospital. 

"  We  wish  a  copy  could  be  put  in  the  hands  of  every  Student  or 
Practitioner  in  the  country.  In  our  estimation,  it  is  the  best  book 
of  the  kind  ever  written." — N.  Y.  Medical  Journal. 

"  Dr.  Waring's  Therapeutics  has  long  been  known  as  one  of  the 
most  thorough  and  valuable  of  medical  works.  The  amount  of 
actual  intellectual  labor  it  represents  is  immense.  .  .  .  An  in- 
dex of  diseases,  with  the  remedies  appropriate  for  their  treatment, 
closes  the  volume." — Boston  Medical  and  Surgical  Reporter. 

"  The  plan  of  this  work  is  an  admirable  one,  and  one  well  calcu- 
lated to  meet  the  wants  of  busy  practitioners.  There  is  a  remark- 
able amount  of  information,  accompanied  with  judicious  comments, 
imparted  in  a  concise  yet  agreeable  style." — Medical  Record. 

No.  7.    MEDICAL  JURISPRUDENCE  AND 
TOXICOLOGY. 

THIRD  REVISED  EDITION. 

By  JOHN  J.  REESE,  M.D.,  Professor  of  Medical  Jurispru- 
dence and  Toxicology  in  the  University  of  Pennsyl- 
vania ;  President  of  the  Medical  Jurisprudence  Society 
of  Phila. ;  Third  Edition,  Revised  and  Enlarged. 

"  This  admirable  text-book." — Amer.Jour.  of  Med.  Sciences. 

"  We  lay  this  volume  aside,  after  a  careful  perusal  of  its  pages, 
with  the  profound  impression  that  it  should  be  in  the  hands  of  every 

doctor  and  lawyer.  It  fully  meets  the  wants  of  all  students 

He  has  succeeded  in  admirably  condensing  into  a  handy  volume  all 
the  essential  points." — Cincinnati  Lancet  and  Clinic. 

"  The  book  before  us  will,  we  think,  be  found  to  answer  the  ex- 
pectations of  the  student  or  practitioner  seeking  a  manual  of  juris- 
prudence, and  the  call  for  a  second  edition  is  a  flattering  testimony 
to  the  value  of  the  author's  present  effort.  The  medical  portion 
of  this  volume  seems  to  be  uniformly  excellent,  leaving  little  for 
adverse  criticism.  The  information  on  the  subject  matter  treated 
has  been  carefully  compiled,  in  accordance  with  recent  knowledge. 
The  lexicological  portion  appears  specially  excellent.  Of  that  por- 
tion of  the  work  treating  of  the  legal  relations  of  the  practitioner 
and  medical  witness,  we  can  express  a  generally  favorable  ver- 
dict."— Physician  and  Surgeon,  Ann  Arbor,  Mich. 

Price  of  each  Book,  Cloth.  $3,00;  Leather,  $3.50. 


6          STUDENTS'  TEXT-BOOKS  AND  MANUALS. 

ANATOMY. 

Macalister's  Human  Anatomy.  816  Illustrations.  A  new 
Text-book  for  Students  and  Practitioners,  Systematic  and  Topo- 
graphical, including  the  Embryology,  Histology  and  Morphology 
of  Man.  With  special  reference  to  the  requirements  of 
Practical  Surgery  and  Medicine.  With  816  Illustrations, 
400  of  which  are  original.  Octavo.  Cloth,  7.50;  Leather,  8.50 
Ballou's  Veterinary  Anatomy  and  Physiology.  Illustrated. 
By  Wm.  R.  Ballou,  M.U.,  Professor  of  Equine  Anatomy  at  New 
York  College  of  Veterinary  Surgeons.  29  graphic  Illustrations. 
i2ino.  Cloth,  i. oo;  Interleaved  for  notes,  1.25 

Holden's  Anatomy.  A  manual  of  Dissection  of  the  Human 
Body.  Fifth  Edition.  Enlarged,  with  Marginal  References  and 
over  200  Illustrations.  Octavo. 

Bound  in  Oilcloth,  for  the  Dissecting  Room,  $4.50. 
"  No  student  of  Anatomy  can  take  up  this  book  without  being 
pleased  and  instructed.  Its  Diagrams  are  original,  striking  and 
suggestive,  giving  more  at  a  glance  than  pages  of  text  description. 
*  *  *  The  text  matches  the  illustrations  in  directness  of  prac- 
tical application  and  clearness  of  detail." — Ne-w  York  Medical 
Record. 

Holden's  Human  Osteology.     Comprising  a  Description  of  the 
Bones,  with  Colored  Delineations  of  the  Attachments   of  the 
Muscles.     The  General  and  Microscopical  Structure  of  Bone  and 
its  Development.    With  Lithographic  Plates  and  Numerous  Illus- 
trations.    Seventh  Edition.     8vo.  Cloth,  6.00 
Holden's  Landmarks,  Medical  and  Surgical.   4th  ed.   Clo.,  1.25 
Heath's  Practical  Anatomy.     Sixth  London  Edition.     24  Col- 
ored Plates,  and  nearly  300  other  Illustrations.  Cloth,  5.00 
Potter's   Compe'nd   of  Anatomy.     Fifth   Edition.     Enlarged. 
16  Lithographic  Plates.     117  Illustrations. 

Cloth,  i.oo;  Interleaved  for  Notes,  1.25 

CHEMISTRY. 

Hartley's  Medical  Chemistry.  Second  Edition.  A  text-book 
prepared  specially  for  Medical,  Pharmaceutical  and  Dental  Stu- 
dents. With  50  Illustrations,  Plate  of  Absorption  Spectra  and 
Glossary  of  Chemical  Terms.  Revised  and  Enlarged.  Cloth,  2. 50 

Trimble.  Practical  and  Analytical  Chemistry.  A  Course  in 
Chemical  Analysis,  by  Henry  Trimble,  Prof,  of  Analytical  Chem- 
istry in  the  Phila.  College  of  Pharmacy.  Illustrated.  Third 
Edition.  8vo.  Cloth,  1.50 

4EJ-  See  pages  2  to  5  for  list  of  Students'  Manuals. 


STUDENTS'  TEXT-BOOKS  AND  MANUALS.         7 

Chemistry  : — Continued. 

Bloxam's  Chemistry,  Inorganic  and  Organic,  with  Experiments. 
Seventh  Edition.  Enlarged  and  Rewritten.  281  Illustrations. 

Cloth,  4.50 ;  Leather,  5.50 

Richter's  Inorganic  Chemistry.  A  text-book  for  Students. 
Third  American,  from  Fifth  German  Edition.  Translated  by 
Prof.  Edgar  F.  Smith,  PH.D.  89  Wood  Engravings  and  Colored 
Plate  of  Spectra.  Cloth,  2.00 

Richter's  Organic  Chemistry,  or  Chemistry  of  the  Carbon 
Compounds.  Illustrated.  Second  Edition.  In  Press. 

Symonds.  Manual  of  Chemistry,  for  the  special  use  of  Medi- 
cal Students.  By  BKANDRETH  SYMONDS,  A.M.,  M.D.,  Asst. 
Physician  Roosevelt  Hospital,  Out- Patient  Department;  Attend- 
ing Physician  Northwestern  Dispensary,  New  York.  i2mo. 

Cloth,  2.00;  Interleaved  for  Notes,  2.40 

Leffmann's  Compend  of  Chemistry.  Inorganic  and  Organic. 
Including  Urinary  Analysis.  Third  Edition.  Revised. 

Cloth,  i.oo;    Interleaved  for  Notes,  1.25 

Leffmann  and  Beam.  Progressive  Exercises  in  Practical 
Chemistry.  i2mo.  Illustrated.  Cloth,  i.oo 

Muter.  Practical  and  Analytical  Chemistry.  Third  Edi- 
tion. Revised  and  Illustrated.  Nearly  Ready. 

Holland.  The  Urine,  Common  Poisons,  and  Milk  Analysis, 
Chemical  and  Microscopical.  For  Laboratory  Use.  Fourth 
Edition,  Enlarged.  Illustrated.  Cloth,  i.oo 

Van  Niiys.     Urine  Analysis.     Illus.  Cloth,  2.00 

Wolff's  Applied  Medical  Chemistry.  By  Lawrence  Wolff, 
M.D.,  Dem.  of  Chemistry  in  Jefferson  Medical  College.  Clo.,  i.oo 

CHILDREN. 

Goodhart  and  Starr.  The  Diseases  of  Children.  Second 
Edition.  By  J.  F.  Goodhart,  M.D.,  Physician  to  the  Evelina 
Hospital  for  Children;  Assistant  Physician  to  Guy's  Hospital, 
London.  Revised  and  Edited  by  Louis  Starr,  M.D.,  Clinical 
Professor  of  Diseases  of  Children  in  the  Hospital  of  the  Univer- 
sity of  Pennsylvania;  Physician  to  the  Children's  Hospital, 
Philadelphia.  Containing  many  Prescriptions  and  Formulae, 
conforming  to  the  U.  S.  Pharmacopoeia,  Directions  for  making 
Artificial  Human  Milk,  for  the  Artificial  Digestion  of  Milk,  etc. 
Illustrated.  Cloth,  3.00;  Leather,  3.50 

Hatfield.  Diseases  of  Children.  By  M.  P.  Hatfield,  M.D., 
Professor  of  Diseases  of  Children,  Chicago  Medical  College. 
Colored  Plate.  i2mo.  Cloth,  i.oo;  Interleaved,  1.25 

4^"  See  pages  14  and  IJ  for  list  of  f  Quiz-  Compends  f 


8          STUDENTS'  TEXT-BOOKS  AND  MANUALS. 

Children:—  Continued. 

Starr.  Diseases  of  the  Digestive  Organs  in  Infancy  and 
Childhood.  With  chapters  on  the  Investigation  of  Disease, 
and  on  the  General  Management  of  Children."  By  Louis  Starr, 
M.D.,  Clinical  Professor  of  Diseases  of  Children  in  the  Univer- 
sity of  Pennsylvania.  Illus.  Second  Edition.  Cloth,  2.25 

DENTISTRY. 

Fillebrown.     Operative  Dentistry.    330  Illus.          Cloth,  2.50 
Flagg's  Plastics  and  Plastic  Filling.     4th  Ed.         Cloth,  4.00 
Gorgas.     Dental  Medicine.    A  Manual  of  Materia  Medica  and 
Therapeutics.     Third  Edition.  Cloth,  3.50 

Harris.  Principles  and  Practice  of  Dentistry.  Including 
Anatomy,  Physiology,  Pathology,  Therapeutics,  Dental  Surgery 
and  Mechanism.  Twelfth  Edition.  Revised  and  enlarged  by 
Professor  Gorgas.  1028  Illustrations.  Cloth,  7.00  ;  Leather,  8.00 
Richardson's  Mechanical  Dentistry.  Fifth  Edition.  569 
Illustrations.  8vo.  Cloth,  4.50;  Leather,  5.50 

Sewill.     Dental  Surgery.    200  Illustrations.     3d  Ed.    Clo.,  3.00 
Taft's  Operative  Dentistry.    Dental  Students  and  Practitioners. 
Fourth  Edition.     100  Illustrations.        Cloth,  4.25  ;  Leather,  5.00 
Talbot.     Irregularities  of  the  Teeth,  and  their  Treatment. 
Illustrated.     8vo.     Second  Edition.  Cloth,  3.00 

Tomes'  Dental  Anatomy.     Third  Ed.     191  Illus.      Cloth,  4.00 
Tomes'  Dental   Surgery.      3d  Edition.      Revised.      292  Illus. 
772  Pages.  Cloth,  5.00 

Warren.  Compend  of  Dental  Pathology  and  Dental  Medi- 
cine. Illustrated.  Cloth,  i.oo;  Interleaved,  1.25 

DICTIONARIES. 

Gould's  New  Medical  Dictionary.  Containing  the  Definition 
and  Pronunciation  of  all  words  in  Medicine,  with  many  useful 
Tables  etc.  %  Dark  Leather,  3.25;  yz  Mor.,  Thumb  Index  4.25 

Harris'  Dictionary  of  Dentistry.  Fifth  Edition.  Completely 
revised  and  brought  up  to  date  by  Prof.  Gorgas. 

Cloth,  5.00;  Leather,  6.00 

Cleaveland's  Pronouncing  Pocket  Medical  Lexicon,  sist 
Edition.  Giving  correct  Pronunciation  and  Definition.  Very 
small  pocket  size.  Cloth,  red  edges  .75  ;  pocket-book  style,  i.oo 

Longley 's  Pocket  Dictionary.  The  Student's  Medical  Lexicon, 
giving  Definition  and  Pronunciation  of  all  Terms  used  in  Medi- 
cine, with  an  Appendix  giving  Poisons  and  Their  Antidotes, 
Abbreviations  used  in  Prescriptions,  Metric  Scale  of  Doses,  etc. 
24mo.  Cloth,  i.oo;  pocket-book  style,  1.25 

j9®=-  See  pages  2  to  5  for  list  of  Students'  Manuals, 


STUDENTS'  TEXT-BOOKS  AND   MANUALS.         9 

EYE. 

Hartridge  on  Refraction.    4th  Ed.  Cloth,  2.00 

Meyer.  Diseases  of  the  Eye.  A  complete  Manual  for  Stu- 
dents and  Physicians.  270  Illustrations  and  two  Colored  Plates. 
8vo.  Cloth,  4.50;  Leather,  5.50 

Swanzy.  Diseases  of  the  Eye  and  their  Treatment.  158 
Illustrations.  Third  Edition.  Cloth,  300 

Fox  and  Gould.  Compend  of  Diseases  of  the  Eye  and 
Refraction.  2d  Ed.  Enlarged.  71  Illus.  39  Formulae. 

Cloth,  i. oo  ;  Interleaved  for  Notes,  1.25 

ELECTRICITY. 

Bigelow.  Plain  Talks  on  Medical  Electricity  and  Batteries. 

Illustrated.  Cloth,  i.oo 

Mason's  Compend  of  Medical   and  Surgical  Electricity. 

With  numerous  Illustrations.     i2mo.  Cloth,  i.oo 

HYGIENE. 

Parkes'  (Ed.  A.)  Practical  Hygiene.  Seventh  Edition,  en- 
larged. Illustrated.  8vo.  Cloth,  4.50 

Parkes'  (L.  C.)  Manual  of  Hygiene  and  Public  Health. 
Second  Edition.  i2mo.  Cloth,  2.50 

Wilson's  Handbook  of  Hygiene  and  Sanitary  Science. 
Seventh  Edition.  Revised  and  Illustrated.  In  Press. 

MATERIA  MEDICA  AND  THERAPEUTICS. 

Potter's  Compend  of  Materia  Medica,  Therapeutics  and 

Prescription  Writing.     Fifth  Edition,  revised  and  improved. 

Cloth,  i.oo;  Interleaved  for  Notes,  1.25 

Biddle's  Materia  Medica.  Eleventh  Edition.  By  the  late 
John  B.  Biddle,  M.D.,  Professor  of  Materia  Medica  in  Jefferson 
Medical  College,  Philadelphia.  Revised,  and  rewritten,  by 
Clement  Biddle,  M.D.,  Assist.  Surgeon,  U.  S.  N.,  assisted  by 
Henry  Morris,  M.D.  8vo.,  illustrated.  Cloth,  4.25;  Leather,  5.00 

Potter.  Materia  Medica,  Pharmacy  and  Therapeutics. 
Including  Action  of  Medicines,  Special  Therapeutics,  Pharma- 
cology, etc.  Second  Edition.  Cloth,  4.00;  Leather,  5.00 

Waring.      Therapeutics.      With  an    Index  of   Diseases    and 
Remedies.     4th  Edition.     Revised.       Cloth,  3.00;  Leather,  3.50 
Jttt"  See  pages  14  and  /jr  for  list  of  TQuiz-Contpends  ? 


10        STUDENTS'  TEXT-BOOKS  AND  MANUALS. 

MEDICAL  JURISPRUDENCE. 
Reese.    A  Text-book  of  Medical  Jurisprudence  and  Toxi- 
cology.    By  John  J.   Reese,  M.D.,  Professor  of  Medical  Juris- 
prudence   and  Toxicology   in   the   Medical  Department  of  the 
University   of  Pennsylvania;     President  of  the  Medical  Juris- 

STidence  Society  of  Philadelphia;    Physician   to  St.  Joseph's 
ospital ;   Corresponding  Member  of  The  New  York  Medico- 
legal  Society.       Third  Edition.  Cloth,  3.00;  Leather,  3.50 

OBSTETRICS  AND  GYNAECOLOGY. 

Byford.  Diseases  of  Women.  The  Practice  of  Medicine  and 
Surgery,  as  applied  to  the  Diseases  and  Accidents  Incident  to 
Women.  By  W.  H.  Byford,  A.M.,  M.D.,  Professor  of  Gynaecology 
in  Rush  Medical  College  and  of  Obstetrics  in  the  Woman's  Med- 
ical College,  etc.,  and  Henry  T.  Byford,  M.D.,  Surgeon  to  the 
Woman's  Hospital  of  Chicago  ;  Gynaecologist  to  St.  Luke's 
Hospital,  etc.  Fourth  Edition.  Revised,  Rewritten  and  En- 
larged. With  306  Illustrations,  over  100  of  which  are  original. 
Octavo.  832  pages.  Cloth,  5.00;  Leather,  6.00 

Cazeaux  and  Tarnier's  Midwifery.  'With  Appendix,  by 
Munde.  The  Theory  and  Practice  of  Obstetrics  ;  including  the 
Diseases  of  Pregnancy  and  Parturition,  Obstetrical  Operations, 
etc.  By  P.  Cazeaux.  Remodeled  and  rearranged,  with  revi- 
sions and  additions,  by  S.  Tarnier,  M.D.,  Professor  of  Obstetrics 
and  Diseases  of  Women  and  Children  in  the  Faculty  of  Medicine 
of  Paris.  Eighth  American,  from  the  Eighth  French  and  First 
Italian  Edition.  Edited  by  Robert  J.  Hess,  M.D.,  Physician  to 
the  Northern  Dispensary,  Philadelphia,  with  an  appendix  by 
Paul  F.  Munde,  M.D.,  Professor  of  Gynaecology  at  the  N.  Y. 
Polyclinic.  Illustrated  by  Chromo-Lithographs,  Lithographs, 
and  other  Full-page  Plates,  seven  of  which  are  beautifully  colored, 
and  numerous  Wood  Engravings.  Students'  Edition.  One 
Vol.,  8vo.  Cloth,  5.00;  Leather,  6.00 

Lewers'  Diseases  of  'Women.  A  Practical  Text-Book.  139 
Illustrations.  Second  Edition.  Cloth,  2.50 

Parvin's  Winckel's  Diseases  of  Women.  Second  Edition. 
Including  a  Section  on  Diseases  of  the  Bladder  and  Urethra. 
150  Illus.  Revised.  Seepages.  Cloth,  3.00 ;  Leather,  3.50 

Morris.    Compend  of  Gynaecology.    Illustrated.      Cloth,  i.oo 

Winckel's  Obstetrics.  A  Text-book  on  Midwifery,  includ- 
ing the  Diseases  of  Childbed.  By  Dr.  F.  Winckel,  Professor 
of  Gynaecology,  and  Director  of  the  Royal  University  Clinic  for 
Women,  in  Munich.  Authorized  Translation,  by  J.  Clifton 
Edgar,  M.D.,  Lecturer  on  Obstetrics,  University  Medical  Col- 
lege, New  York,  with  nearly  200  handsome  illustrations,  the 
majority  of  which  are  original  with  this  work.  Octavo. 

Cloth,  6.00;  Leather,  7.00 

Landis'  Compend  of  Obstetrics.  Illustrated.  4th  edition, 
enlarged.  Cloth,  i.oo;  Interleaved  for  Notes,  1.25 

JKg~  See  pages  2  to  5  for  list  of  New  Manuals. 


STUDENTS'  TEXT-BOOKS  AND  MANUALS.         11 

Obstetrics  and  Gyncecology  : —  Continued. 

Galabin's   Midwifery.      By  A.    Lewis   Galabin,   M.D.,  F.R.C.P. 

227  Illustrations.     Seepages.  Cloth,  3.00;  Leather,  3.50 

Rigby's  Obstetric  Memoranda.    4th  Edition.  Cloth,  .50 

Swayne's  Obstetric  Aphorisms.  For  the  use  of  Students 
commencing  Midwifery  Practice.  8th  Ed.  i2mo.  Cloth,  1.25 

PATHOLOGY.    HISTOLOGY.    BIOLOGY. 

Bowlby.  Surgical  Pathology  and  Morbid  Anatomy,  for 
Students.  135  Illustrations.  i2mo.  Cloth,  2.00 

Davis'  Elementary  Biology.     Illustrated.  Cloth,  4.00 

Gilliam's  Essentials  of  Pathology.  A  Handbook  for  Students. 
47  Illustrations.  i2mo.  Cloth,  2.00 

*^*The  object  of  this  book  is  to  unfold  to  the  beginner  the  funda- 
mentals of  pathology  in  a  plain,  practical  way,  and  by  bringing 
them  within  easy  comprehension  to  increase  his  interest  in  the  study 
of  the  subject. 

Gibbes'  Practical  Histology  and  Pathology.    Third  Edition. 

Enlarged.     i2mo.  Cloth,  1.75 

Virchow's  Post-Mortem  Examinations,    sd  Ed.    Cloth,  i.oo 

PHYSIOLOGY. 

Yeo's  Physiology.  Fifth  Edition.  The  most  Popular  Stu- 
dents' Book.  By  Gerald  F.  Yeo,  M.D.,  F.R.C.S.,  Professor  of 
Physiology  in  King's  College,  London.  Small  Octavo.  758 
pages.  321  carefully  printed  Illustrations.  With  a  Full 
Glossary  and  Index.  See  Page 3.  Cloth,  3.00;  Leather,  3.50 

Brubaker's  Compend  of  Physiology.  Illustrated.  Sixth 
Edition.  Cloth,  i.oo;  Interleaved  for  Notes,  1.25 

Stirling.  Practical  Physiology,  including  Chemical  and  Ex- 
perimental Physiology.  142  Illustrations.  "  Cloth,  2.25 

Kirke's  Physiology.  New  i2th  Ed.  Thoroughly  Revised  and 
Enlarged.  502  Illustrations.  Cloth,  4.00 ;  Leather,  5.00 

Landois'  Human  Physiology.  Including  Histology  and  Micro- 
scopical Anatomy,  and  with  special  reference  to  Practical  Medi- 
cine. Third  Edition.  Translated  and  Edited  by  Prof.  Stirling. 
692  Illustrations.  Cloth,  6.50;  Leather,  7.50 

"  With  this  Text-book  at  his  command,  no  student  could  fail  in 

his  examination." — Lancet, 

Sanderson's  Physiological  Laboratory.  Being  Practical  Ex- 
ercises for  the  Student.  350  Illustrations.  8vo.  Cloth,  5.00 

PRACTICE. 

Taylor.  Practice  of  Medicine.  A  Manual.  By  Frederick 
Taylor,  M.D.,  Physician  to,  and  Lecturer  on  Medicine  at,  Guy's 
Hospital,  London  ;  Physician  to  Evelina  Hospital  for  Sick  Chil- 
dren, and  Examiner  in  Materia  Medica  and  Pharmaceutical 
Chemistry,  University  of  London.  Cloth,  4.00 ;  Leather,  5.00 

4®-  See  pages  14  and  13  for  list  of  ?  Quiz-  Compends  f 


12        STUDENTS'   TEXT-BOOKS  AND   MANUALS. 

Practice  : — Continued. 

Roberts'  Practice.  New  Revised  Edition.  A  Handbook 
of  the  Theory  and  Practice  of  Medicine.  By  Frederick  T. 
Roberts,  M.D.  ;  M.R.C.P.,  Professor  of  Clinical  Medicine  and 
Therapeutics  in  University  College  Hospital,  London.  Seventh 
Edition.  Octavo.  Cloth,  5.50 ;  Sheep,  6.50 

Hughes.  Compend  of  the  Practice  of  Medicine.  4th  Edi- 
tion. Two  parts,  each,  Cloth,  i.oo;  Interleaved  for  Notes,  1.25 
PART  i. — Continued,  Eruptive  and  Periodical  Fevers,  Diseases 

of  the  Stomach,  Intestines,   Peritoneum,  Biliary  Passages,  Liver, 

Kidneys,  etc.,  and  General  Diseases,  etc. 

PART   n. — Diseases   of  the   Respiratory   System,   Circulatory 

System  and  Nervous  System  ;  Diseases  of  the  Blood,  etc. 
Physicians'  Edition.    Fourth  Edition.    Including  a  Section 
on  Skin  Diseases.  With  Index,    i  vol.  Full  Morocco,  Gilt,  2.50 

From  John  A.  Robinson,  M.D.,  Assistant^  to  Chair  of  Clinical 
Medicine,  now  Lecturer  on  Mater ia  Medica,  Rush  Medical  Col- 
lege, Chicago. 
"  Meets  with   my  hearty  approbation   as   a  substitute  for  the 

ordinary  note  books  almost  universally  used  by  medical  students. 

It  is  concise,  accurate,  well  arranged  and  lucid,     .     .     .    just  the 

thing  for  students  to  use  while  studying  physical  diagnosis  and  the 

more  practical  departments  of  medicine." 

PRESCRIPTION   BOOKS. 

Wythe's  Dose  and  Symptom  Book.  Containing  the  Doses 
and  Uses  of  all  the  principal  Articles  of  the  Materia  Medica,  etc. 
Seventeenth  Edition.  Completely  Revised  and  Rewritten.  Just 
Ready.  32mo.  Cloth,  i.oo;  Pocket-book  style,  1.25 

Pereira's  Physician's  Prescription  Book.  Containing  Lists 
of  Terms,  Phrases,  Contractions  and  Abbreviations  used  in 
Prescriptions  Explanatory  Notes,  Grammatical  Construction  ot 
Prescriptions,  etc.,  etc.  By  Professor  Jonathan  Pereira,  M.D. 
Sixteenth  Edition.  32mo.  Cloth,  i.oo;  Pocket-book  style,  1.25 

PHARMACY. 

Stewart's  Compend  of  Pharmacy.  Based  upon  Remington's 
Text-Book  of  Pharmacy.  Third  Edition,  Revised.  With  new 
Tables,  Index,  Etc.  Cloth,  i.oo  ;  Interleaved  for  Notes,  1.25 

Robinson.  Latin  Grammar  of  Pharmacy  and  Medicine. 
By  H.  D.  Robinson,  PH.D.,  Professor  of  Latin  Language  and 
Literature,  University  of  Kansas,  Lawrence.  With  an  Intro- 
duction by  L.  E.  Sayre,  PH.G.,  Professor  of  Pharmacy  in,  and 
Dean  of,  the  Dept.  of  Pharmacy,  University  of  Kansas.  i2mo. 

Cloth,  2.00 

SKIN  DISEASES. 

Anderson,  (McCall)  Skin  Diseases.  A  complete  Text-Book, 
with  Colored  Plates  and  numerous  Wood  Engravings.  8vo. 

Cloth,  4.50;  Leather,  5.50 

Van  Harlingen  on  Skin  Diseases.  A  Handbook  of  the  Dis- 
eases of  the  Skin,  their  Diagnosis  and  Treatment  (arranged  alpha- 
betically). By  Arthur  Van  Harlingen,  M.D.,  Clinical  Lecturer 
on  Dermatology,  Jefferson  Medical  College ;  Prof,  of  Diseases  of 
the  Skin  in  the  Philadelphia  Polyclinic.  2d  Edition.  Enlarged. 
With  colored  and  other  plates  and  illustrations.  i2mo.  Cloth,  2.50 
ee  pages  2  to  5  for  list  of  New  Manuals. 


STUDENTS'  TEXT-BOOKS  AND  MANUALS.        IS 

SURGERY   AND    BANDAGING. 

Moullin's  Surgery,  A  new  Text-Book.  500  Illustrations,  200  of 
which  are  original.  Cloth,  7.00;  Leather,  8.00 

Jacobson.  Operations  in  Surgery.  A  Systematic  Handbook 
for  Physicians,  Students  and  Hospital  Surgeons;  By  W.  H.  A. 
Jacobson,  B  A.,  Oxon.  F.R.C.S.  Eng.;  Ass't  Surgeon  Guy's  Hos- 
pital ;  Surgeon  at  Royal  Hospital  for  Children  and  Women,  etc. 
199  Illustrations.  1006  pages.  8vo.  Cloth.  5.00 ;  Leather,  6.00 

Heath's  Minor  Surgery,  and  Bandaging.  Ninth  Edition.  142 
Illustrations.  60  Formulae  and  Diet  Lists.  Cloth,  2.00 

Horwitz's  Compend  of  Surgery,  Minor  Surgery  and 
Bandaging,  Amputations,  Fractures,  Dislocations,  Surgical 
Diseases,  and  the  Latest  Antiseptic  Rules,  etc.,  with  Differential 
Diagnosis  and  Treatment.  By  ORVILLE  HOKWITZ,  B.S.,  M.D., 
Demonstrator  of  Surgery,  Jefferson  Medical  College.  4th  edition. 
Enlarged  and  Rearranged.  136  Illustrations  and  84  Formulae. 
12010.  Cloth,  i.oo ;  Interleaved  for  the  addition  of  Notes,  1.25 

***  The  new  Section  on  Bandaging  and  Surgical  Dressings,  con- 
sists of  32  Pages  and  41  Illustrations.  Every  Bandage  of  any 
importance  is  figured.  This,  with  the  Section  on  Ligation  ol 
Arteries,  forms  an  ample  Text-book  for  the  Surgical  Laboratory. 

Walsham.  Manual  of  Practical  Surgery.  For  Students  and 
Physicians.  By  WM.  J.  WALSHAM,  M.D.,  F.R.C.S.,  Asst.  Surg. 
to,  and  Dem.  of  Practical  Surg.  in,  St.  Bartholomew's  Hospital, 
Surgeon  to  Metropolitan  Free  Hospital,  London.  With  236 
Engravings.  See  Page  2.  Cloth,  3.00;  Leather,  3.50 

URINE,  URINARY   ORGANS,  ETC. 

Holland.  The  Urine,  and  Common  Poisons  and  The 
Milk.  Chemical  and  Microscopical,  for  Laboratory  Use.  Illus- 
trated. Fourth  Edition.  i2mo.  Interleaved.  Cloth,  i.oo 

Ralfe.  Kidney  Diseases  and  Urinary  Derangements.  42  Illus- 
trations. i2mo.  572  pages.  Cloth,  2.75 

Marshall  and  Smith.  On  the  Urine.  The  Chemical  Analysis  of 
the  Urine.  By  John  Marshall,  M.D.,  Chemical  Laboratory,  Univ. 
of  Penna ;  and  Prof.  E.  F.  Smith,  PH.D.  Col.  Plates.  Cloth,  i.oo 

Tyson.  On  the  Urine.  A  Practical  Guide  to  the  Examination 
of  Urine.  With  Colored  Plates  and  Wood  Engravings.  7th  Ed. 
Enlarged.  i2mo.  Cloth,  1.50 

Van  Niiys,  Urine  Analysis.    Illus.  Cloth,  2.00 


VENEREAL  DISEASES. 

>per.    Student's  Manual  of  Venere 
Tulae.     Fourth  Edition.     i2mo. 

4&~  See  pages  14  and ij  for  list  of  f  Qmt-Compends  f 


Hill  and  Cooper.    Student's  Manual  of  Venereal  Diseases, 
with  Formulae.     Fourth  Edition.     i2mo.  Cloth,  i.oo 


NEW  AND  REVISED  EDITIONS. 

PQUIZ-COMPENDS? 

The  Best  Compends  for  Students'  Use 

in  the  Quiz  Class,  and  when  Pre- 

paring for  Examinations. 

Compiled  in  accordance  with  the  latest  teachings  of  promi- 

nent lecturers  and  the  most  popular  Text-books. 
They  form  a  most  complete,  practical  and  exhaustive 
set  of  manuals,  containing  information  nowhere  else  col- 
lected in  such  a  condensed,  practical  shape.  Thoroughly 
up  to  the  times  in  every  respect,  containing  many  new 
prescriptions  and  formulae,  and  over  two  hundred  and 
fifty  illustrations,  many  of  which  have  been  drawn  and 
engraved  specially  for  this  series.  The  authors  have  had 
large  experience  as  quiz-masters  and  attaches  of  colleges, 
with  exceptional  opportunities  for  noting  the  most  recent 
advances  and  methods. 

Cloth,  each  $1.00.  Interleaved  for  Notes,  $1.25. 
No.  x.  HUMAN  ANATOMY,  "  Based  upon  Gray."  Fifth 
Enlarged  Edition,  including  Visceral  Anatomy,  formerly 
published  separately.  16  Lithograph  Plates,  New 
Tables  and  117  other  Illustrations.  By  SAMUEL  O.  L. 
POTTER,  M.A.,  M.D.,  M.R.C.P.  (Lond.,)  late  A.  A.  Surgeon  U.  S. 
Army.  Professor  of  Practice,  Cooper  Medical  College,  San  Fran- 
cisco. 

Nos.  2  and  3.  -PRACTICE  OF  MEDICINE.    Fourth  Edi- 
tion.    By  DANIEL  E.  HUGHES,  M.D.,  Demonstrator  of  Clinical 
Medicine  in  Jefferson  Medical  College,  Philadelphia.  In  two  parts. 
PART  I.  —  Continued,  Eruptive  and  Periodical  Fevers,  Diseases 
of  the  Stomach,  Intestines,  Peritoneum,  Biliary  Passages,  Liver, 
Kidneys,  etc.  (including  Tests  for  Urine),  General  Diseases,  etc. 


,        .  ,  ,        . 

PART  II.  —  Diseases  of  the  Respiratory  System  (including  Phy- 
scal Diagnosis),  Circulatory  System  and  Nervous  System;  Dis- 
eases of  the  Blood,  etc. 


*#*  These  little  books  can  be  regarded  as  a  full  set  of  notes  upon 
the  Practice  of  Medicine,  containing  the  Synonyms,  Definitions, 
Causes,  Symptoms,  Prognosis,  Diagnosis,  Treatment,  etc.,  of  each 
disease,  and  including  a  number  of  prescriptions  hitherto  unpub- 
lished. 

No.  4.  PHYSIOLOGY,  including  Embryology.  Sixth 
Edition.  By  ALBERT  P.  BRUBAKER,  M.D.,  Prof,  of  Physiology, 
Penn'a  College  of  Dental  Surgery  ;  Demonstrator  of  Physiology 
in  Jefferson  Medical  College,  Philadelphia.  Revised,  Enlarged, 
with  new  Illustrations. 

No.  5.  OBSTETRICS.  Illustrated.  Fourth  Edition.  By 
HENRY  G.  LANDIS,  M.D.,  Prof,  of  Obstetrics  and  Diseases  of 
Women,  in  Starling  Medical  College,  Columbus,  O.  Revised 
Edition.  New  Illustrations. 


BLAKISTON'S  ?  QUIZ-COMPENDS  ? 

No.  6.  MATERIA  MEDICA,  THERAPEUTICS  AND 
PRESCRIPTION  WRITING.  Fifth  Revised  Edition. 

With  especial  Reference  to  the  Physiological  Action  of  Drugs, 
and  a  complete  article  on  Prescription  Writing.  Based  on  the 
Last  Revision  of  the  U.  S.  Pharmacopoeia,  and  including  many 
unofficial  remedies.  By  SAMUEL  O.  L.  POTTER,  M.A.,  M.D., 
M.R.C.P.  (Lond.,)  late  A.  A.  Surg.  U.  S.  Army ;  Prof,  of  Practice, 
Cooper  Medical  College,  San  Francisco.  Improved  and  Enlarged, 
with  Index. 

No.  7.  GYNAECOLOGY.  A  Compend  of  Diseases  of  Women. 
By  HENRY  MORRIS,  M.D.,  Demonstrator  of  Obstetrics,  Jefferson 
Medical  College,  Philadelphia.  45  Illustrations. 

No.  8.  DISEASES  OF  THE  EYE  AND  REFRACTION, 
including  Treatment  and  Surgery.  By  L.  WEBSTER  Fox,  M.D., 
Chief  Clinical  Assistant  Ophthalmological  Dept.,  Jefferson  Med- 
ical College,  etc.,  and  GEO.  M.  GOULD,  M.D.  71  Illustrations,  39 
Formulae.  Second  Enlarged  and  Improved  Edition.  Index. 

No.  9.  SURGERY,  Minor  Surgery  and  Bandaging.  Illus- 
trated. Fourth  Edition.  Including  Fractures,  Wounds, 
Dislocations,  Sprains,  Amputations  and  other  operations  ;  Inflam- 
mation, Suppuration,  Ulcers,  Syphilis,  Tumors,  Shock,  etc. 
Diseases  of  the  Spine,  Ear,  Bladder,  Testicles,  Anus,  and 
other  Surgical  Diseases.  By  ORVILLE  HORWITZ,  A.M.,  M.D., 
Demonstrator  of  Surgery,  Jefferson  Medical  College.  Revised 
and  Enlarged.  84  Formulae  and  136  Illustrations. 

No.  10.  CHEMISTRY.  Inorganic  and  Organic.  For  Medical 
and  Dental  Students.  Including  Urinary  Analysis  and  Medical 
Chemistry.  By  HENRY  LEFFMANN,  M.D.,  Prof,  of  Chemistry  in 
Penn'a  College  of  Dental  Surgery,  Phila.  Third  Edition,  Revised 
and  Rewritten,  with  Index. 

No.  ii.  PHARMACY.  Based  upon  "  Remington's  Text-book 
of  Pharmacy."  By  F.  E.  STEWART,  M.D. ,  PH. G.,  Quiz-Master 
at  Philadelphia  College  of  Pharmacy.  Third  Edition,  Revised. 

No.  12.  VETERINARY  ANATOMY  AND  PHYSIOL- 
OGY. 29  Illustrations.  By  WM.  R.  BALLOU,  M.D.,  Prof,  of 
Equine  Anatomy  at  N.  Y.  College  of  Veterinary  Surgeons. 

No.  13.  DENTAL  PATHOLOGY  AND  DENTAL  MEDI- 
CINE. Containing  all  the  most  noteworthy  points  of  interest 
to  the  Dental  student.  By  GEO.  W.  WARREN,  D.D.S.,  Clinical 
Chief,  Penn'a  College  of  Dental  Surgery,  Philadelphia.  Illus. 

No.  14.  DISEASES  OF  CHILDREN.  By  DR.  MARCUS  P. 
HATFIELD,  Prof,  of  Diseases  of  Children,  Chicago  Medical 
College.  Colored  Plate. 

Bound  in  Cloth,  $1.    Interleaved,  for  the  Addition  of  Notes,  $1.25. 

Jg^0  These  books  are  constantly  revised  to  keep  up  -with 
the  latest  teachings  and  discoveries,  so  that  they  contain 
all  the  new  methods  and  principles.  No  series  of  books 
are  so  complete  in  detail^  concise  in  language ',  or  so  well 
printed  and  bound.  Each  one  forms  a  complete  set  of 
notes  upon  the  subject  under  consideration. : 
Illustrated  Descriptive  Circular ( 


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COMPACT. 

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PRACTICAL. 

ACCURATE. 

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UP  TO  DATE. 


It  contains  Tables  of  the  Arteries,  Bacilli,  Gan- 
glia,   Leucomames,    Micrococci,    Muscles, 
Nerves,    Plexuses,    Ptomaines,    etc., 
etc.,  that  will  be  found  of  great 
use  to  the    student. 


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From  J.  M.  DACOSTA,  M.  D.,  Professor  of  Practice  and 
Clinical  Medicine,  Jefferson  Medical  College,  Philadelphia. 

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A    UNIQUE    BOOK. 


POTTER'S  MATERIA  MEDICA,  PHARMACY  AND  THERA- 
PEUTICS. Second  Edition.  Revised  and  Enlarged.  A  Hand- 
book;  including  the  Physiological  Action  of  Drugs,  Special  Therapeutics 
of  Diseases,  Official  and  Extemporaneous  Pharmacy,  etc.  By  S.  O.  L. 
POTTER,  M.A.,  M.D.,  Professor  of  the  Practice  of  Medicine  in  Cooper 
Medical  College,  San  Francisco;  Late  A.  A.  Surgeon,  U.  S.  Army,  etc. 
A  new  Edition  in  larger  type.  Octavo.  Cloth,  $4.00;  Leather,  $5.00. 

DR.  POTTER  has  become  well  known  as  an  able  compiler,  by  his  Compends 
of  Anatomy,  and  of  Materia  Medica,  both  of  which  have  reached  four  editions. 
In  this  book,  more  elaborate  in  its  design,  he  has  shown  his  literary  abilities  to 
much  better  advantage,  and  all  who  examine  or  use  it  will  agree  that  he  has 
produced  a  work  containing  more  correct  information  in  a  practical,  concise 
form  than  any  other  publication  of  the  kind.  The  plan  of  the  work  is  new, 
and  its  contents  have  been  combined  and  arranged  in  such  a  way  that  it  offers 
a  compact  statement  of  the  subject  in  hand. 

PART  I. — MATERIA  MEDICA  and  THERAPEUTICS,  the  drugs  being  arranged 
in  alphabetical  order,  with  the  synonym  of  each  first;  then  the  description  of 
the  plant,  its  preparations,  physiological  action,  and  lastly  its  Therapeutics. 
This  part  is  preceded  by  a  section  on  the  classification  of  medicines  as  follows: 
Agents  acting  on  the  Nervous  System,  Organs  of  Sense,  Respiration,  Circu- 
lation, Digestive  System,  on  Metabolism  (including  Restoratives,  Alteratives, 
Astringents,  Antipyretics,  Antiphlogistics  and  Antiperiodics,  etc.).  Agents  act- 
ing upon  Excretion,  the  Generative  System,  the  Cutaneous  Surfaces,  Microbes 
and  Ferments,  and  upon  each  other. 

PART  II. — PHARMACY  AND  PRESCRIPTION  WRITING.  Written  for  the  use 
of  physicians  who  put  up  their  own  prescriptions.  It  includes — Weights  and 
Measures,  English  and  the  Metric  Systems.  Specific  Gravity  and  Volume. 
Prescriptions. — Their  principles  and  combinations ;  proper  methods  of  writing 
them;  abbreviations  used,  etc.  Stock  solutions  and  preparations,  such  as  a 
doctor  should  have  to  compound  his  own  prescriptions.  Incompatibility, 
Pharmaceutical  and  Therapeutical.  Liquid,  Solid  and  Gaseous  Extempo- 
raneous Prescriptions. 

PART  III. — SPECIAL  THERAPEUTICS,  an  alphabetical  List  of  Diseases — a 
real  INDEX  OF  DISEASES — giving  the  drugs  that  have  been  found  serviceable 
in  each  disease,  and  the  authority  recommending  the  use  of  each ;  a  very  im- 
portant feature,  as  it  gives  an  authoritative  character  to  the  book  that  is  unusual 
in  works  on  Therapeutics,  and  displays  an  immense  amount  of  research  on  the 
part  of  the  author.  600  prescriptions  are  given  in  this  part,  many  being  over 
the  names  of  eminent  men. 

THE  APPENDIX  contains  lists  of  Latin  words,  phrases  and  abbreviations,  with 
their  English  equivalents,  used  in  medicine,  Genitive  Case  Endings,  etc.  36 
Formulae  for  Hypodermic  Injections;  a  comparison  of  10  Formulae  of  Chloro- 
dyne;  Formulae  of  prominent  patent  medicines;  Poisons  and  their  Antidotes; 
Differential  Diagnosis ;  Notes  on  Temperature  in  Disease ;  Obstetrical  Memo- 
randa; Clinical  Examination  of  Urine;  Medical  Ethics;  Table  of  Specific 
Gravities  and  Volumes ;  Table  showing  the  number  of  drops  in  a  fluidrachm 
of  various  liquids  and  the  weight  of  one  fluidrachm  in  grains,  and  a  table  for 
converting  apothecaries'  weights  and  measures  into  grams. 


A  MINE  OF  WEALTH  FOR  THE  STUDENT. 


Standard  Text-Books. 

LANDOIS'  HUMAN  PHYSIOLOGY.  A  Text-Book  of  Human  Physi- 
ology, including  Histology  and  Microscopical  Anatomy,  with  special 
reference  to  the  requirements  of  Practical  Medicine.  By  Dr.  L. 
LANDOIS,  Professor  of  Physiology  and  Director  of  the  Physiological  Insti- 
tute, University  of  Greifswald.  Translated  from  the  Fifth  German  Edition, 
with  additions  by  WM.  STIRLING,  M.D.,  SC.D,,  Brackenburg,  Professor  of 
Physiology  and  Histology  in  Owen's  College  and  Victoria  University,  Man- 
chester; Examiner  in  the  Honors'  School  of  Science,  University  of  Ox- 
ford, England.  Third  Edition,  revised  and  enlarged.  692  Illustrations. 
One  Volume.  Royal  Octavo.  Cloth,  $6.50;  Leather,  $7.50. 

"  With  this  Text-book  at  command,  NO  STUDENT  COULD  FAIL  IN  HIS  EXAMINATION."  — 
Tlu  Lancet. 

"  One  of  the  MOST  PRACTICAL  WORKS  on  Physiology  ever  written,  forming  a  '  bridge  '  be- 
tween Physiology  and  Practical  Medicine.  .  .  .Its  chief  merits  are  its  completeness  and 
conciseness.  .  .  .  EXCELLENTLY  CLEAR,  ATTRACTIVE  AND  SUCCINCT."  —  British  Medical 
Journal. 

"  Unquestionably  the  most  admirable  exposition  of  the  relations  of  Human  Physiology  to 
Practical  Medicine  ever  laid  before  English  readers."—  Students'  Journal. 

"  Landois'  Physiology  is,  without  question,  the  best  text-book  on  the  subject  that  has  ever 
been  written."—  W«*  York  Medical  Record. 


CAZEAUX  AND  TARNIER'S  MIDWIFERY.  Eighth  Revised 
and  Enlarged  Edition.  With  Appendix,  by  Munde.  The  Theory 
and  Practice  of  Obstetrics;  including  the  Diseases  of  Pregnancy  and 
Parturition,  Obstetrical  Operations,  etc.  By  P.  CAZEAUX,  Member  of 
the  Imperial  Academy  of  Medicine.  Remodeled  and  rearranged,  with 
revisions  and  additions,  by  S.  TARNIER,  M.D.,  Prof,  of  Obstetrics  and 
Diseases  of  Women  and  Children  in  the  Faculty  of  Medicine  of  Paris. 
Eighth  American,  from  the  Eighth  French  and  First  Italian  Editions. 
Edited  and  Enlarged  by  ROBERT  J.  HESS,  M.D.,  Physician  to  the  Northern 
Dispensary,  Phila.,  etc.,  with  an  Appendix  by  PAUL  F.  MUNDE,  M.D., 
Professor  of  Gynaecology  at  the  New  York  Poly  clinic,  Vice  -President 
American  Gynaecological  Society,  etc.  With  Chromo-Lithographs,  Litho- 
graphs, and  other  Full-page  Plates,  seven  of  which  are  beautifully  colored, 
and  numerous  Wood  Engravings.  One  Volume,  octavo. 

Cloth,  $5.00;    Full  Leather,  £6.00. 

MEYER  ON  DISEASES  OF  THE  EYE.  ,„  ...^nual  of  Ophthal- 
mology. By  Dr.  EDOUARD  MEYER,  Prof,  a  1'Ecole  Pratique  de  la  Faculte 
Medecine  de  Paris;  Chevalier  of  the  Legion  of  Honor,  etc.  Translated 
from  the  Third  French  Edition,  with  the  assistance  of  the  author,  by  Dr. 
FREELAND  FERGUS,  Assistant  Surgeon,  Glasgow  Eye  Infirmary.  With  267 
Illustrations  and  three  Colored  Plates.  Prepared  under  the  direction  of  Dr. 
R.  Liebreich.  8vo.  Cloth,  $4.50;  Leather,  $5.50. 

The  first  chapter  is  an  explanation  of  the  best  means  for  examining  the  eyes, 
externally  and  internally,  with  a  view  to  diagnosis,  the  various  ophthalmo- 
scopes, general  considerations  on  the  treatment  of  ophthalmia,  etc.  Each  dis- 
ease is  then  taken  up  in  its  proper  order;  the  anatomy  of  the  part  being  pre- 
sented first,  followed  by  the  diagnosis,  causes,  progress,  prognosis,  etiology  and 
Jreatment.  The  arrangement  of  the  work  will  thus  be  seen  to  be  systematic, 
commending  itself  to  all  physicians  and  students  for  the  logical  and  concise 
way  in  which  the  facts  are  given.  This  English  edition  makes  the  eighth 
language  into  which  Meyer's  book  has  been  translated. 

P.  BLAKISTON,  SON   &  CO.,  Publishers  and   Booksellers, 
1012  WALNUT  STREET,  PHILADELPHIA, 


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Standard  Text-Books. 


HOLDEN'S  ANATOMY.  A  Manual  of  the  Dissections  of  the  Human 
Body.  By  LUTHER  HOLDEN,  F.R.C.S.  Fifth  Edition.  Carefully  Revised 
and  Enlarged,  specially  concerning  the  Anatomy  of  the  Nervous  System  /- 
Organs  of  Special  Sense,  etc.  By  JOHN  LANGTON,  F.R.C.S.,  Surgeon  to, 
and  Lecturer  on  Anatorry  at,  St.  Bartholomew's  Hospital.  208  Illustrations. 
8vo.  Cloth,  $$.00-,  Leather,  $6.00. 

Oil-cloth  Covers,  for  the  Dissecting  Room,  $4.50. 

The  popularity  of  this  work  has  steadily  increased  during  the  past  few  years.  It  is  proba- 
bly used  more  extensively  than  any  other  dissector.  The  Oil-cloth  binding  allows  of  wash- 
ing, and  does  not  retain  the  dirt  and  odor  of  the  dissecting  table.  This  edition  has  been 
carefully  printed  and  bound,  and  lays  open  flat  at  any  page. 

"  No  student  of  anatomy  can  take  up  this  book  without  being  pleased  and  instructed.    Its 


diagrams  are  original,  striking  and   suggestive,  giving  more  at  a  glance  than  pages  of  text 

ith  this 
stuy  and  r 
these  points  be  emphasized  to  such  as  are  commencing  their  studies.     The  text  matches  the 


description.     All  this  is  known  to   those  who  are  already  acquainted  with  this  admirable 
work  ;  but  it  is  simpe  justice  to  its  value,  as  a  work  for  careful  study  and  reference,  that 


illustrations  in  directness  of  practical  application  and  clearness  of  detail."  —  New  York  Med- 
ical Record. 

ANDERSON  ON  SKIN  DISEASES.  A  complete  Treatise  on  Skin 
Diseases.  By  McCALL  ANDERSON,  M.D.,  Professor  of  Clinical  Medicine, 
University  of  Glasgow.  With  numerous  wood  engravings  and  several  col- 
ored and  steel  plates.  Octavo.  Cloth,  $4.50.  Leather,  $5.50.  Just  Ready. 

This  aims  to  be  a  complete  text-book.  It  will  be  found  to  contain  all  the  latest  methods 
of  treatment.  The  subject  is  dealt  with  in  a  systematic,  practical  manner,  and  is  based  on 
an  extensive  experience  of  nearly  twenty-five  yean. 

GOWERS'  MANUAL  OF  DISEASES  OF  THE  NERVOUS 
SYSTEM.  A  Complete  Text-book.  By  WILLIAM  R.  GOWERS,  M.D., 
Professor  Clinical  Medicine,  University  College,  London.  Physician  to 
National  Hospital  for  the  Paralyzed  and  Epileptic.  Comprising  over 
400  Illustrations  and  1  360  pages.  Octavo.  Cloth,  $6.50;  Leather,  $7.50. 

BYFORD.  DISEASES  OF  WOMEN.  The  Practice  of  Medicine  and 
Surgery,  as  applied  to  the  Diseases  and  Accidents  Incident  to  Women. 
By  W.  H.  BYFORD,  A.M.,  M.D.,  Professor  of  Gynaecology  in  Rush  Medical 
College  and  of  Obstetrics  in  the  Woman's  Medical  College  ;  Surgeon  to 
the  Woman's  Hospital;  Ex-  President  American  Gynaecological  Society, 
etc.  ;  and  HENRY  T.  BYFORD,  M.D.,  Surgeon  to  the  Woman's  Hospital 
of  Chicago  ;  Gynaecologist  to  St.  Luke's  Hospital  ;  President  Chicago 
Gynaecological  Society,  etc.  Fourth  Edition,  Revised,  Rewritten  and 
Enlarged.  With  306  Illustrations,  over  100  of  which  are  original.  Octavo. 
832  pages.  Cloth,  $5.00;  Leather,  $6.00. 

"  In  short,  the  book  is  brought  up  to  the  standard  of  to-day,  and  in  most  respects  may  be 
considered  a  reliable,  practical  text-book,  written  by  an  earnest  worker  anp)  practical  man." 
<—  American  Journal  of  Medical  Sciences. 

ROBERTS.  PRACTICE  OF  MEDICINE.  The  Theory  and  Prac- 
tice of  Medicine.  By  FREDERICK  ROBERTS,  M.D.,  Professor  of  Thera- 
peutics at  University  College,  London.  Seventh  American  Edition, 
thoroughly  revised  and  enlarged,  with  new  Illustrations.  8vo.  Cloth, 
£5.50;  Leather,  #6.50. 

"  If  there  is  a  book  in  the  whole  of  medical  literature  in  which  so  much  is  said  in  so  few 
words,  it  has  never  come  within  our  reach."  —  Chicago  Medical  Journal. 

"  The  best  text-book  for  students.  We  know  of  no  work  in  the  English  language,  or  of 
•By  other,  which  competes  with  this  one."—  Edinburgh  Medical  Journal. 

P.  BLAKISTON,  SON  &  CO.,  Publishers  and  Books«ll«rs. 
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